diff --git a/CHANGES b/CHANGES
index 7eba3029a0d..719de31ce1a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -16,6 +16,8 @@ Deprecated
   Use ``hashlib`` instead.
 * #11526: Deprecate ``sphinx.testing.path``.
   Use ``os.path`` or ``pathlib`` instead.
+* #11528: Deprecate ``sphinx.util.split_index_msg`` and ``sphinx.util.split_into``.
+  Use ``sphinx.util.index_entries.split_index_msg`` instead.
 
 Features added
 --------------
diff --git a/doc/extdev/deprecated.rst b/doc/extdev/deprecated.rst
index 71bfad02e4d..b5662ae183c 100644
--- a/doc/extdev/deprecated.rst
+++ b/doc/extdev/deprecated.rst
@@ -22,6 +22,16 @@ The following is a list of deprecated interfaces.
      - Removed
      - Alternatives
 
+   * - ``sphinx.util.split_into``
+     - 7.2
+     - 9.0
+     - N/A
+
+   * - ``sphinx.util.split_index_msg``
+     - 7.2
+     - 9.0
+     - ``sphinx.util.index_entries.split_index_msg``
+
    * - ``sphinx.testing.path``
      - 7.2
      - 9.0
diff --git a/sphinx/builders/gettext.py b/sphinx/builders/gettext.py
index d0acdc77ac2..fda5f2463bc 100644
--- a/sphinx/builders/gettext.py
+++ b/sphinx/builders/gettext.py
@@ -18,10 +18,11 @@
 from sphinx.builders import Builder
 from sphinx.errors import ThemeError
 from sphinx.locale import __
-from sphinx.util import logging, split_index_msg
+from sphinx.util import logging
 from sphinx.util.console import bold  # type: ignore
 from sphinx.util.display import status_iterator
 from sphinx.util.i18n import CatalogInfo, docname_to_domain
+from sphinx.util.index_entries import split_index_msg
 from sphinx.util.nodes import extract_messages, traverse_translatable_index
 from sphinx.util.osutil import canon_path, ensuredir, relpath
 from sphinx.util.tags import Tags
diff --git a/sphinx/domains/index.py b/sphinx/domains/index.py
index 3715907487f..21536349ccc 100644
--- a/sphinx/domains/index.py
+++ b/sphinx/domains/index.py
@@ -11,8 +11,9 @@
 from sphinx import addnodes
 from sphinx.domains import Domain
 from sphinx.environment import BuildEnvironment
-from sphinx.util import logging, split_index_msg
+from sphinx.util import logging
 from sphinx.util.docutils import ReferenceRole, SphinxDirective
+from sphinx.util.index_entries import split_index_msg
 from sphinx.util.nodes import process_index_entry
 from sphinx.util.typing import OptionSpec
 
diff --git a/sphinx/environment/adapters/indexentries.py b/sphinx/environment/adapters/indexentries.py
index e9b2fe7b8d4..1cbf4a2d238 100644
--- a/sphinx/environment/adapters/indexentries.py
+++ b/sphinx/environment/adapters/indexentries.py
@@ -11,7 +11,8 @@
 from sphinx.environment import BuildEnvironment
 from sphinx.errors import NoUri
 from sphinx.locale import _, __
-from sphinx.util import logging, split_into
+from sphinx.util import logging
+from sphinx.util.index_entries import _split_into
 
 logger = logging.getLogger(__name__)
 
@@ -41,20 +42,20 @@ def create_index(self, builder: Builder, group_entries: bool = True,
                 try:
                     if entry_type == 'single':
                         try:
-                            entry, sub_entry = split_into(2, 'single', value)
+                            entry, sub_entry = _split_into(2, 'single', value)
                         except ValueError:
-                            entry, = split_into(1, 'single', value)
+                            entry, = _split_into(1, 'single', value)
                             sub_entry = ''
                         _add_entry(entry, sub_entry, main,
                                    dic=new, link=uri, key=category_key)
                     elif entry_type == 'pair':
-                        first, second = split_into(2, 'pair', value)
+                        first, second = _split_into(2, 'pair', value)
                         _add_entry(first, second, main,
                                    dic=new, link=uri, key=category_key)
                         _add_entry(second, first, main,
                                    dic=new, link=uri, key=category_key)
                     elif entry_type == 'triple':
-                        first, second, third = split_into(3, 'triple', value)
+                        first, second, third = _split_into(3, 'triple', value)
                         _add_entry(first, second + ' ' + third, main,
                                    dic=new, link=uri, key=category_key)
                         _add_entry(second, third + ', ' + first, main,
@@ -62,11 +63,11 @@ def create_index(self, builder: Builder, group_entries: bool = True,
                         _add_entry(third, first + ' ' + second, main,
                                    dic=new, link=uri, key=category_key)
                     elif entry_type == 'see':
-                        first, second = split_into(2, 'see', value)
+                        first, second = _split_into(2, 'see', value)
                         _add_entry(first, _('see %s') % second, None,
                                    dic=new, link=False, key=category_key)
                     elif entry_type == 'seealso':
-                        first, second = split_into(2, 'see', value)
+                        first, second = _split_into(2, 'see', value)
                         _add_entry(first, _('see also %s') % second, None,
                                    dic=new, link=False, key=category_key)
                     else:
diff --git a/sphinx/search/__init__.py b/sphinx/search/__init__.py
index 5d20a514939..21758d3f424 100644
--- a/sphinx/search/__init__.py
+++ b/sphinx/search/__init__.py
@@ -16,7 +16,7 @@
 
 from sphinx import addnodes, package_dir
 from sphinx.environment import BuildEnvironment
-from sphinx.util import split_index_msg
+from sphinx.util.index_entries import split_index_msg
 
 if TYPE_CHECKING:
     from collections.abc import Iterable
diff --git a/sphinx/transforms/i18n.py b/sphinx/transforms/i18n.py
index ceb9e241235..f6bad514321 100644
--- a/sphinx/transforms/i18n.py
+++ b/sphinx/transforms/i18n.py
@@ -18,8 +18,9 @@
 from sphinx.locale import __
 from sphinx.locale import init as init_locale
 from sphinx.transforms import SphinxTransform
-from sphinx.util import get_filetype, logging, split_index_msg
+from sphinx.util import get_filetype, logging
 from sphinx.util.i18n import docname_to_domain
+from sphinx.util.index_entries import split_index_msg
 from sphinx.util.nodes import (
     IMAGE_TYPE_NODES,
     LITERAL_TYPE_NODES,
diff --git a/sphinx/util/__init__.py b/sphinx/util/__init__.py
index 72f1101b1e9..105ecb38ccc 100644
--- a/sphinx/util/__init__.py
+++ b/sphinx/util/__init__.py
@@ -16,6 +16,7 @@
 from sphinx.util import display as _display
 from sphinx.util import exceptions as _exceptions
 from sphinx.util import http_date as _http_date
+from sphinx.util import index_entries as _index_entries
 from sphinx.util import logging
 from sphinx.util import osutil as _osutil
 from sphinx.util.console import strip_colors  # NoQA: F401
@@ -220,30 +221,6 @@ def parselinenos(spec: str, total: int) -> list[int]:
     return items
 
 
-def split_into(n: int, type: str, value: str) -> list[str]:
-    """Split an index entry into a given number of parts at semicolons."""
-    parts = [x.strip() for x in value.split(';', n - 1)]
-    if len(list(filter(None, parts))) < n:
-        raise ValueError(f'invalid {type} index entry {value!r}')
-    return parts
-
-
-def split_index_msg(entry_type: str, value: str) -> list[str]:
-    # new entry types must be listed in util/nodes.py!
-    if entry_type == 'single':
-        try:
-            return split_into(2, 'single', value)
-        except ValueError:
-            return split_into(1, 'single', value)
-    if entry_type == 'pair':
-        return split_into(2, 'pair', value)
-    if entry_type == 'triple':
-        return split_into(3, 'triple', value)
-    if entry_type in {'see', 'seealso'}:
-        return split_into(2, 'see', value)
-    raise ValueError(f'invalid {entry_type} index entry {value!r}')
-
-
 def import_object(objname: str, source: str | None = None) -> Any:
     """Import python object by qualname."""
     try:
@@ -300,6 +277,9 @@ def _xml_name_checker():
     'format_exception_cut_frames': (_exceptions.format_exception_cut_frames,
                                     'sphinx.exceptions.format_exception_cut_frames'),
     'xmlname_checker': (_xml_name_checker, 'sphinx.builders.epub3._XML_NAME_PATTERN'),
+    'split_index_msg': (_index_entries.split_index_msg,
+                        'sphinx.util.index_entries.split_index_msg'),
+    'split_into': (_index_entries.split_index_msg, 'sphinx.util.index_entries.split_into'),
     'md5': (_md5, ''),
     'sha1': (_sha1, ''),
 }
diff --git a/sphinx/util/index_entries.py b/sphinx/util/index_entries.py
new file mode 100644
index 00000000000..fb2d15a4d71
--- /dev/null
+++ b/sphinx/util/index_entries.py
@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+
+def split_index_msg(entry_type: str, value: str) -> list[str]:
+    # new entry types must be listed in util/nodes.py!
+    if entry_type == 'single':
+        try:
+            return _split_into(2, 'single', value)
+        except ValueError:
+            return _split_into(1, 'single', value)
+    if entry_type == 'pair':
+        return _split_into(2, 'pair', value)
+    if entry_type == 'triple':
+        return _split_into(3, 'triple', value)
+    if entry_type in {'see', 'seealso'}:
+        return _split_into(2, 'see', value)
+    raise ValueError(f'invalid {entry_type} index entry {value!r}')
+
+
+def _split_into(n: int, type: str, value: str) -> list[str]:
+    """Split an index entry into a given number of parts at semicolons."""
+    parts = [x.strip() for x in value.split(';', n - 1)]
+    if len(list(filter(None, parts))) < n:
+        raise ValueError(f'invalid {type} index entry {value!r}')
+    return parts
diff --git a/sphinx/writers/latex.py b/sphinx/writers/latex.py
index d4441987807..994e5291602 100644
--- a/sphinx/writers/latex.py
+++ b/sphinx/writers/latex.py
@@ -20,8 +20,9 @@
 from sphinx.domains.std import StandardDomain
 from sphinx.errors import SphinxError
 from sphinx.locale import _, __, admonitionlabels
-from sphinx.util import logging, split_into, texescape
+from sphinx.util import logging, texescape
 from sphinx.util.docutils import SphinxTranslator
+from sphinx.util.index_entries import split_index_msg
 from sphinx.util.nodes import clean_astext, get_prev_node
 from sphinx.util.template import LaTeXRenderer
 from sphinx.util.texescape import tex_replace_map
@@ -1688,37 +1689,32 @@ def style(string: str) -> str:
             if ismain:
                 m = '|spxpagem'
             try:
+                parts = tuple(map(escape, split_index_msg(type, string)))
+                styled = tuple(map(style, parts))
                 if type == 'single':
                     try:
-                        p1, p2 = (escape(x) for x in split_into(2, 'single', string))
-                        P1, P2 = style(p1), style(p2)
+                        p1, p2 = parts
+                        P1, P2 = styled
                         self.body.append(fr'\index{{{p1}@{P1}!{p2}@{P2}{m}}}')
                     except ValueError:
-                        p = escape(split_into(1, 'single', string)[0])
-                        P = style(p)
+                        p, = parts
+                        P, = styled
                         self.body.append(fr'\index{{{p}@{P}{m}}}')
                 elif type == 'pair':
-                    p1, p2 = (escape(x) for x in split_into(2, 'pair', string))
-                    P1, P2 = style(p1), style(p2)
-                    self.body.append(r'\index{%s@%s!%s@%s%s}\index{%s@%s!%s@%s%s}' %
-                                     (p1, P1, p2, P2, m, p2, P2, p1, P1, m))
+                    p1, p2 = parts
+                    P1, P2 = styled
+                    self.body.append(fr'\index{{{p1}@{P1}!{p2}@{P2}{m}}}'
+                                     fr'\index{{{p2}@{P2}!{p1}@{P1}{m}}}')
                 elif type == 'triple':
-                    p1, p2, p3 = (escape(x) for x in split_into(3, 'triple', string))
-                    P1, P2, P3 = style(p1), style(p2), style(p3)
+                    p1, p2, p3 = parts
+                    P1, P2, P3 = styled
                     self.body.append(
-                        r'\index{%s@%s!%s %s@%s %s%s}'
-                        r'\index{%s@%s!%s, %s@%s, %s%s}'
-                        r'\index{%s@%s!%s %s@%s %s%s}' %
-                        (p1, P1, p2, p3, P2, P3, m,
-                         p2, P2, p3, p1, P3, P1, m,
-                         p3, P3, p1, p2, P1, P2, m))
-                elif type == 'see':
-                    p1, p2 = (escape(x) for x in split_into(2, 'see', string))
-                    P1 = style(p1)
-                    self.body.append(fr'\index{{{p1}@{P1}|see{{{p2}}}}}')
-                elif type == 'seealso':
-                    p1, p2 = (escape(x) for x in split_into(2, 'seealso', string))
-                    P1 = style(p1)
+                        fr'\index{{{p1}@{P1}!{p2} {p3}@{P2} {P3}{m}}}'
+                        fr'\index{{{p2}@{P2}!{p3}, {p1}@{P3}, {P1}{m}}}'
+                        fr'\index{{{p3}@{P3}!{p1} {p2}@{P1} {P2}{m}}}')
+                elif type in {'see', 'seealso'}:
+                    p1, p2 = parts
+                    P1, _P2 = styled
                     self.body.append(fr'\index{{{p1}@{P1}|see{{{p2}}}}}')
                 else:
                     logger.warning(__('unknown index entry type %s found'), type)