WASHINGTON, Dec. 13 (Xinhuanet) -- A U.S. stem cell expert has asked for the removal of his name from the landmark research of human cloning by controversial South Korean scientist Woo Suk Hwang, according to a document released on Tuesday.

    In a letter to the journal of Science, Dr. Gerald Schatten, scientist of the University of Pittsburgh, demanded that the journal take his name off a human cloning study published by Woo Suk Hwang and colleagues at Seoul National University in May of 2005.

    "My careful re-evaluations of published figures and tables, along with new problematic information, now casts substantial doubts about the paper's accuracy," said Schatten in the letter released by his university.

    "Over the weekend, I received allegations from someone involved with the experiments that certain elements of the report may be fabricated," Schatten said, giving no further comment on the issue.

    Hwang and his colleagues made history in 2004 when they reported they had cloned the first human embryo to derive embryonic stem cells for scientific and medical research.

    In May of 2005 they reported they had cloned cells from people with diseases, to make batches of cells useful for studying those diseases. And in August they reported that they had cloned the first dog, Snuppy.

    Science declined to remove Schatten's name, listed as a senior researcher, from the 25 authors of the paper.

    "There is no method for retracing authorship," said the journal in a statement.

    "As of this writing, Science is not aware of any scientists claiming that the data are fraudulent," it added.

    A number of international scientists have called on Hwang to submit his controversial work to independent analysts for scientific confirmation.

    Seoul National University official Roe Jung-hye said on Monday that experts from the university would start an investigation and conduct DNA tests on Hwang's tailored stem cell lines. Enditem