The president of the government-backed Riken institute admitted Friday there were "grave errors" in two papers produced by its researchers on a possible method to create pluripotent stem cells but wouldn't say whether the alleged irregularities were intentional.

Separately Friday, Haruko Obokata, lead author of the two papers on potentially groundbreaking stem cell research, and two of her co-authors, released a statement in which they said they are looking into the possibility of withdrawing the papers.

The papers, written by 14 Japanese and U.S. researchers about a procedure to reprogram stem cells, were published in the British science journal Nature in late January. If the papers are withdrawn, the findings themselves will also be retracted.