Reporter jailed for refusing to identify source

US district judge Thomas Hogan said Ms Miller should be imprisoned immediately and stay behind bars until she changes her mind, or until the grand jury ends its term in October.

Speaking outside the courthouse in Washington, Bill Keller, the executive editor of the Times, warned that the ruling could open a new era of legal pressure on journalists.

A second journalist involved in the case, Matthew Cooper of Time magazine, had been set to be jailed until he told the judge that he had just been given a "specific, personal and unambiguous" waiver by his source to reveal his (or her) identity to the grand jury. A week before, Time had agreed to surrender Mr Cooper's notes to the grand jury, over the objections of its reporter.

Mr Cooper's move is particularly intriguing. Last weekend, it emerged that during his work on the story, he had spoken to Karl Rove, President George Bush's top political adviser when the leak occurred, in the summer of 2003.

A lawyer for Mr Rove, who is now deputy chief of staff at the White House, has acknowledged that his client spoke to Mr Cooper, but maintains he did not reveal the name of the CIA operative, Valerie Plame.

The investigation into the leak has become convoluted. Robert Novak, the columnist who first published Ms Plame's name, seems to have escaped scotfree. Ms Miller never even wrote a story about the affair, but is now going to jail.

She had no choice but to protect her source, she said. "If journalists cannot be trusted to keep confidences, then journalists cannot function and there cannot be a free press."

Ms Plame is the wife of former US ambassador Joseph Wilson, who claims her name was leaked by someone in the Bush administration to punish him for his accusation that the White House deliberately twisted intelligence in the run-up to the Iraq invasion of March 2003.

Explaining his decision yesterday, Judge Hogan said that by ordering Ms Miller to jail, her source might be persuaded to give her a more specific waiver of confidentiality, as had happened in the case of Mr Cooper.