Judith Miller, the New York Times reporter who went to jail instead of testifying in court about a CIA leak case related to the Iraq war, was released from detention after agreeing to testify before a grand jury in the investigation, the newspaper reported online.

Miller, who spent more than 12 weeks in the Virginia detention centre, said that her source had released her from her reporter's pledge of confidentiality to protect the source's name.

Miller and another journalist, Matthew Cooper of Time magazine, originally refused to reveal the name of sources who provided them with the identity of an undercover CIA officer.

The officer, Valerie Plame, is married to a key figure in the Iraq weapons of mass destruction scandal, and revealing of her identity was seen as payback for her husband's public revelations that countermanded assertions by US President George W. Bush.

Plame's husband, former ambassador Joe Wilson, had been sent by the Bush administration to Niger in February 2002 to check a claim that Iraq had tried to buy yellow cake uranium from the north African country.

Wilson reported back that the suspicion was unfounded, but the dramatic claim still made it into Bush's 2003 State of the Union address and helped garner support for the war in Iraq.

Later revelations uncovered a trail of forged documents that had been used to make it appear that Niger had sold yellow cake ore to Iraq - documents which US security agents originally verified as authentic.

Wilson's public revelations that he had told the White House he could not substantiate the suspicions about Niger kicked off a further storm over Bush's overstated claims that Iraq had weapons of mass destruction, and needed to be invaded. The weapons were never found.

Wilson has asserted that the leak of his wife's identity as a CIA officer came from the White House in retaliation for his outspoken criticism of how the Bush administration had made false allegations.

Unveiling the identity of an undercover intelligence officer is a crime, but the reporters said their First Amendment rights protect them from prosecution for their failure to reveal the sources.

Miller, who never wrote an article about Plame, and Cooper were rebuffed by the US Supreme Court, where they sought protection under the First Amendment of the US Constitution.