Nobel laureate Ryoji Noyori, head of the Riken institute, intends to step down after a difficult year caused by last year's botched stem cell study, sources close to the matter said.

Noyori, 76, won the 2001 Nobel Prize in chemistry and has been president of Riken since October 2003. He cited the length of his tenure at the state-backed institute as the reason for quitting, the sources said Friday.

Noyori has been leading efforts to reform the country's leading research organization since researcher Haruko Obokata was found to have engaged in research misconduct when she published her attention-grabbing papers on the creation of so-called STAP cells.

Stimulus-triggered acquisition of pluripotency (STAP) cells were initially hailed as a potentially groundbreaking phenomenon in regenerative medicine after the papers appeared in the British science journal Nature in January last year. But the papers were retracted in July after critical errors were found in the study. Obokata, 31, left the institute after she and fellow scientists failed to reproduce her findings.

Noyori voluntarily returned a portion of his pay last year to take responsibility over the scandal. He is now in his third term, which was supposed to end in March 2018. The head of Riken is appointed by the minister of education, culture, sports, science and technology.