A court in Washington has held a reporter in contempt for refusing to testify in an investigation into the exposure of an undercover CIA agent.
The jury is probing any link between the leak and the White House
The court ruled Time magazine reporter Matthew Cooper must testify to the grand jury investigating the leaking of agent Valerie Plame's name.
Investigators are probing claims government officials were involved.
Ms Plame's husband says her name was leaked in retribution for his article challenging the government over Iraq.
US District Judge Thomas F Hogan ruled that Mr Cooper and Tim Russert, the host of NBC Television's Meet the Press, must testify "regarding alleged conversations they had with a specified executive branch official".
The reporters had tried to avoid the grand jury subpoena on the grounds it violated the First Amendment of the Constitution's guarantee of a free press.
However, the judge said there was no such privilege in the case of "a grand jury acting in good faith".
NBC News said Mr Russert was no longer required to testify as he had been interviewed under oath by prosecutors on Saturday.
The name was leaked a week after her husband's article
But the contempt order instructs that Mr Cooper be detained and Time fined $1,000 a day until he complies.
Those penalties have been suspended pending appeals.
Several leading government officials have already testified to the grand jury or been interviewed by prosecutors - among them Secretary of State Colin Powell, national security adviser Condoleezza Rice and former CIA director George Tenet.
President George W Bush himself was interviewed in June at the White House.
Ms Plame's husband, former US charge d'affaires in Baghdad, Joseph Wilson, had been sent by the CIA to Niger to investigate claims that then Iraqi leader Saddam Hussein had tried to obtain uranium for nuclear weapons.
He concluded there was no evidence but Mr Bush still referred to the claims in his State of the Union address.
A week after Mr Wilson's article appeared questioning the policy on the Niger allegations, Ms 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 later 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.
Disclosing a covert agent's name is a criminal offence in the US, punishable by up to 10 years in prison.