Stem cell pioneer Hwang Woo-suk is said to have fabricated the results of his thesis on stem cells.

Roh Sung-il, who collaborated on the paper published in the U.S. magazine Science, told KBS and other news media Thursday that nine of the eleven stem cell lines mentioned in the paper were fakes and that the authenticity of the other two is questionable.

Roh, a board member of MizMedi Hospital in Seoul, said Hwang on Thursday admitted to major flaws in his paper published in June.

Roh also said that a scientist working in Hwang's lab was pressured to make embryos look like clones.

Roh said he and Hwang agreed to ask Science to withdraw the paper.

Hwang's paper was hailed as a breakthrough, with many predicting it would lead to cures for a host of degenerative diseases.