US President George W Bush has welcomed a Justice Department investigation into claims White House staff illegally blew the cover of a CIA agent.
Bush says he wants the truth to come out
In his first public remarks on the affair, Mr Bush urged anyone with information to come forward, saying: "I want to know the truth."
It is alleged that administration officials leaked the name of the agent - the wife of a former US diplomat - in revenge for his claims that intelligence officials exaggerated the case for war in Iraq.
Correspondents say it is extremely rare for the Department of Justice to conduct a full investigation into the alleged leaking of classified information.
Disclosing a covert agent's name is a criminal offence in the US, punishable by up to 10 years in prison.
White House staff were notified by e-mail on Tuesday that the Justice Department had decided to move from a preliminary investigation to a full-blown inquiry.
Staff were told to "preserve all materials that might in any way be related to the department's investigation".
These are likely to include telephone logs, e-mails, notes and other documents.
Speaking in Chicago, President Bush said he had told his staff to co-operate with the inquiry.
"This investigation is a good thing," he said.
"If there is a leak out of my administration, I want to know who it is. If the person has violated law, that person will be taken care of."
Act of revenge?
The allegations centre around the naming of Valerie Plame, wife of Joseph Wilson, the former US charge d'affaires in Baghdad.
Before the war in Iraq, Mr Wilson was sent by the CIA to the West African state of Niger in order to investigate claims that Iraq had tried to buy nuclear material there.
His report concluded that there was no evidence for the claims.
Despite this, Mr Bush referred to them in his State of the Union address in January.
In a subsequent article in the New York Times, Mr Wilson questioned why his report had been ignored.
The White House later admitted it had been a mistake to include the claim in the address.
A week after Mr Wilson's article appeared, Valerie Plame was exposed by journalist Robert Novak, who said he based his report on two unidentified senior administration officials.
A report in the Washington Post newspaper has suggested that White House officials blew the cover of Mr Wilson's wife in order to discredit him, by suggesting he had been given the Niger mission only at her urging.