British science journal Nature said Thursday it had failed to learn from a past instance of research misconduct, a day after it retracted two stem cell papers that were widely condemned as substandard.

It said it accepted the papers on "stimulus-triggered acquisition of pluripotency," or STAP for short, on the reputation of their Japanese authors.

"For scientists worldwide it has triggered painful memories of a decade-old scandal," the journal said.

In 2004, South Korean researcher Woo Suk Hwang said he had generated stem cell lines from cloned human embryos, a claim that was exposed as a fabrication the following year.

"Among stem cell researchers, STAP has become another cautionary tale to add to Hwang's, with its own set of lessons," Nature said.

The two STAP papers were headed by Haruko Obokata, a largely unknown young researcher, and co-authored by noted stem-cell researchers including Yoshiki Sasai and Teruhiko Wakayama.

Published in January, the papers said mouse cells with STAP could be obtained through an astonishingly simple laboratory process, and that they were capable of developing into any type of tissue.

Obokata reported that she had converted the mouse cells to an embryonic-like state merely by soaking them in mildly acidic liquid.

The STAP process was "so contrary to current thinking that some scientists said they accepted it based only on the reputation of Obokata's co-authors, who were some of the most trusted names in stem-cell research and cloning," the journal said.

The Japanese government-affiliated Riken research institute, to which Obokata belongs, recommended the retraction after identifying problems with images published in the papers.

Nature quoted its spokeswoman as saying the journal does not check the images in all papers because of limitations in resources and that the images in Obokata's papers were not checked.