Is there a way to restart figure numbering in Sphinx?

Question

I have a set of three related documents in Sphinx (4.2.0). The top-level table of contents looks like this:

.. toctree::
   :maxdepth: 2

   Requirements_Specification/index.rst
   User_Guide/index.rst
   Release_Report/index.rst

In conf.py, I have:

numfig = True
numfig_secnum_depth = 1

This numbers all the figures and tables consecutively across the three documents. For example, if there are 10 figures in each document, then:

• the figures in the Requirements Specification doc are numbered 1 to 10
• the figures in the User Guide doc are numbered 11 to 20
• the figures in the Release Report doc are numbered 21 to 30.

Instead, I would like the numbering to start at 1 in each doc, so in this example each doc would have figures numbered 1 to 10. Is there some way of achieving this?

I've tried putting :numbered: in the toctree directive, but that treats each doc as a chapter (i.e. Requirements Specification is chapter 1, User Guide is chapter 2, Release Report is chapter 3). I need each doc to be able to stand alone. I build the docs both as one set of HTML and also as three separate PDFs.