Someone other than the co-authors of the controversial papers on STAP cells may have succeeded last week in reproducing the alleged discovery by lead author Haruko Obokata, the government-funded Riken institute said Monday, cautioning the results have yet to be proved.

"Someone other than co-authors of the papers confirmed work by 'versatile' genes," a Riken public relations officer said, adding it cannot disclose the person's name. "But it's not a complete replication (of STAP) and does not back up Ms. Obokata's claim."

The lead author of the papers on stimulus-triggered acquisition of pluripotency cells disputes the April 1 conclusion of her employer, Riken, that she falsified and fabricated parts of the disputed work.

The papers appeared in January in the journal Nature.

Obokata, 30, said her team made STAP cells that can grow into any mouse body tissue more than 200 times.

Obokata said Riken recognizes the person who reproduced the cells, but she did not name the person at the press conference last Wednesday, where she admitted improperly using an image to show a result in her experiment. She said her findings remain valid and that she will not agree to withdraw the papers.

Riken plans to decide later this week whether to reinvestigate the papers as she has requested. If it declines, Riken's conclusion will become final and it might take disciplinary action against her.

On Monday, Obokata issued a statement through her lawyer saying she "produced STAP cells almost every day and often a few times in one day."

It said the cells were created over 100 times through September 2011 and over 100 times afterward for her experiments.