U.S. scientists are calling unusual the request of American researcher Gerald Schatten that his name be dropped from a paper he co-authored with stem cell pioneer Hwang Woo-suk.

The journal Science, which published the paper, has rejected the request in that it cannot retract a published report based simply on the request of a co-author.

The magazine's editors also said Schatten is in no position to request a retraction because as a co-author, he could also face a probe if problems are found in the paper.

Johns Hopkins University researcher John Gierhart said Schatten cannot avoid responsibility because he should have reviewed all aspects of the report before signing on as a co-author.