Citing in the bibliography of a separate document

I’m trying to cite references in a supplementary information file from the bibliography (using bibtex) of a main text file. Can I do this so as to use the same numbering is an the main text and keeping them as separate documents (just one bib for the main text)?

I have xr working fine between the two for figure panel cross-referencing, but this doesn’t seem to work for citations (xcite seems to have now been replaced by xr, but I’m not sure it could this anyway).