The head of an investigative panel at the state-backed Riken institute that found one of its scientists guilty of research misconduct over the contested discovery of "STAP cells" resigned as chairman Friday amid allegations his own research paper contains falsifications.

Riken began a preliminary probe into the allegations, a move likely to affect the appeal process initiated by accused scientist Haruko Obokata, who was judged by the panel to have fabricated and falsified data in her papers on so-called STAP cells.

Shunsuke Ishii, a senior scientist who heads Riken's Molecular Genetics Laboratory, said on his lab's website that in a paper published in the cancer journal Oncogene in 2008, some images had been cut and pasted so their order would match the explanations given in the text. He was one of the principal authors of the cancer gene paper.