A panel questioned stem cell researcher Hwang Woo-suk, sealed off his office and secured materials in his laboratory Sunday as it began a probe of allegations he falsified embryonic stem cells that he said he had created in a scientific breakthrough.

Seoul National University began the investigation after Hwang acknowledged there were "fatal errors" in a May article in the journal Science claiming that he and other researchers cloned human embryos and created 11 stem cell lines that genetically matched certain patients.

Scientists hope to use such "therapeutic cloning" someday to create tissue for transplant into people with illnesses like diabetes and Parkinson's disease.

Hwang said Friday he had asked Science to withdraw the paper.

The university where Hwang works said in a statement Sunday that it also was questioning his fellow researchers and reviewing their materials.

Hwang's research made him a national hero in South Korea and spurred thousands of people to volunteer skin cells to help him launch a global center to grow embryonic stem cells for research.

Hwang acknowledged the faults in his work a day after co-author Roh Sung-il said Thursday that Hwang had pressured another scientist to fake data for the report.

Roh alleged nine of the 11 cell lines were faked and the authenticity of the other two was unknown.

In a nationally televised news conference, Hwang said only eight stem cell lines existed when he submitted the paper for review but his team later created three more. He insisted tests on his stem cell lines will prove his team "has the source technology to produce them."

Hwang claimed some of the stem cell colonies his team created have been replaced by those created by Roh's hospital and called for an investigation. Roh said Hwang was trying to deflect the controversy onto a former colleague who works at the hospital.

Hwang's team had told Science that multiple photos of the same stem cell lines were accidentally submitted as separate colonies, a mistake the editors have said did not affect the findings.

Hwang's list of achievements includes the world's first cloned human embryos and the world's first cloned dog, the Afghan hound Snuppy.

Last month, he admitted he used eggs from two female scientists in his lab, in violation of ethics guidelines. He then stepped down as head of his research center, the World Stem Cell Hub.

After that revelation, many South Koreans rallied behind Hwang. Hundreds of women volunteered to donate eggs for the research and some of his supporters threatened a TV show that was reporting on the controversy.