BBC Washington Correspondent Tom Carver reports

An American magazine, Star, says it is trying to establish whether the president is the father of a 13-year-old boy of mixed race from Little Rock, Arkansas.

The boy's mother is a black prostitute, Bobbie Anne Williams, who has alleged for some time that the president is the boy's father. She used to work the streets near the governor's mansion in Little Rock at the time Mr Clinton was state governor.

She says her son is the product of a $300 sex session with him.

Presidential resemblance

The president denies ever meeting the woman, although her son, called Danny Williams, is said to resemble Bill Clinton as a boy.

The White House says it does not comment on tabloid stories

The story was investigated by right-wingers in 1992, when Mr Clinton was running for president. They said they believed the allegations, but were not able to substantiate them.

DNA testing - which has already caused so much trouble for Mr Clinton with Monica Lewinsky's infamous semen-stained dress - could finally prove whether or not he is the boy's father.

Star Magazine says it is now trying to see whether Danny Williams's DNA has any link with Mr Clinton's DNA polymarkers, which were published in the Starr report.

No conclusive proof

DNA experts say that if there is a match, it will only suggest there is an 85-95% certainty that Mr Clinton is the father. That is insufficient in American courts to conclusively prove paternity.

Malcolm Brabant: Clinton can resolve this by authorising the FBI to release his DNA details

The White House has not responded to the story. It says it does not comment on tabloid articles.

There is no indication when the results will be published, but the story is another potential time bomb for the Clinton presidency.

Some analysts believe the president could not survive being labelled what Americans call a "dead-beat Dad" - a father who abandons his child - especially after recent initiatives aimed at clamping down on parents who avoid child support.