Miller has spent almost three months in jail

Miller was freed after a source said she could discuss their conversations and she is now expected to appear on Friday morning before a grand jury.

The case concerns the unmasking of a CIA agent, Valerie Plame, in 2003.

Ms Plame's husband was a former diplomat who had criticised President Bush over Iraq, and it was alleged a White House source leaked her name.

The disclosure of a CIA agent's name can be a federal offence.

Joseph Wilson, Ms Plame's husband, had earlier attacked President George W Bush over evidence he had presented to justify the assault on Iraq.

Mr Wilson later alleged that his wife's name was deliberately leaked in revenge.

Waiver offer

Special Counsel Patrick Fitzgerald wanted to jail both Miller and another reporter, Matthew Cooper of Time magazine.

But in early July Cooper changed his mind, and agreed to testify. Miller refused to do so, and was jailed. She has spent 86 days behind bars.

The New York Times says that Miller has now received permission from a source to testify about her conversations with him.

"My source has now voluntarily and personally released me from my promise of confidentiality regarding our conversations," said Miller in a statement.

The "direct and uncoerced" waiver was offered "voluntarily and personally", the newspaper reported.

US Constitution

The New York Times says that source is I Lewis "Scooter" Libby, who is chief of staff to Vice President Dick Cheney.

Miller and Libby met and talked by telephone in July 2003, the paper says.

The leak of Ms Plame's name was not made to Cooper or Miller, but they came to the attention of the prosecutor because of their inquiries.

The grand jury probe has focused particularly on the week in which Miller had conversations with her White House source.

In July, Miller and Cooper had refused to co-operate with the investigation, claiming they should not have to reveal their sources because of press freedoms guaranteed in the US Constitution.

That defence was over-ruled by a court in Washington.