James Watson has not yet issued a comment on the development.

A Nobel Prize-winning American scientist who co-discovered DNA has been stripped of his honourary titles after repeating racist comments in a documentary.

James Watson, who discovered the double-helix structure of DNA alongside Francis Crick in the 1950s based on the work of British chemist Rosalind Franklin, said in a PBS film that genes cause a difference in intelligence between white and black people in IQ tests, CNN reported today.

The 90-year-old's comments were labelled "reprehensible" by the Cold Spring Harbour Laboratory (CSHL) on New York's Long Island, where Watson had been the director from 1968 to 1993.

The laboratory said on Sunday that it "unequivocally rejects the unsubstantiated and reckless personal opinions Dr. James D Watson expressed", noting the statements were "reprehensible (and) unsupported by science". "The Laboratory condemns the misuse of science to justify prejudice," it added.

Mr Watson has not yet issued a comment on the development.

Mr Watson previously told Britain's Sunday Times newspaper in 2007 that he was "inherently gloomy about the prospect of Africa" because "all our social policies are based on the fact that their intelligence is the same as ours, whereas all the testing says not really".

The scientist added that while he hoped everyone was equal, "people who have to deal with black employees find this is not true".

Those comments led CSHL to relieve him of his administrative duties, but he retained his honourary titles until now.

While Watson apologised for the comments in 2007, he said in the PBS documentary American Masters: Decoding Watson, which aired on January 2, that his views had not changed.

The remarks are the latest in a series of racist and homophobic statements that have tainted Watson's career, CNN reported.