The White House has strongly denied allegations that it deliberately revealed the identity of an undercover CIA agent.
Media reports in the US suggest that the identity of the female agent was revealed to punish her husband, a former senior diplomat, for casting doubt on the Bush administration's claims about Iraq's nuclear programme.
As the former envoy to Iraq, Joe Wilson was the last American diplomat to meet Saddam Hussein, in 1991.
The CIA sent him to Niger last year, to investigate claims that Saddam Hussein had tried to buy yellowcake uranium there. He concluded it was unlikely.
Despite this, the allegation appeared in President Bush's State of the Union address last January.
Mr Wilson publicly questioned why his report was ignored, and claimed the administration was twisting the facts to suit its policy.
Reports now suggest that in July a senior White House official called several journalists urging them to carry stories that would reveal the identity of Mr Wilson's wife, a CIA agent.
The CIA has asked the Justice Department to investigate, but Democrats are calling for an independent inquiry.
