Lewis Libby has been an influential figure in the White House

Lewis Libby, chief-of-staff to Dick Cheney, was also charged with obstruction of justice and making false statements to a federal grand jury.

Bush aide Karl Rove was not charged but the investigation remains open.

The identity of CIA agent Valerie Plame - whose husband criticised the Iraq war - was leaked to a US reporter in 2003.

Mr Libby said he was confident he would be "completely and totally exonerated".

Special prosecutor Patrick Fitzgerald has accused Mr Libby of lying to investigators about how and when he learned and disclosed to reporters classified information about Ms Plame.

LEWIS LIBBY INDICTMENT Two charges of perjury Two counts of making a false statement One charge of obstruction of justice Indictment in full (110kb) Most computers will open PDF documents automatically, but you may need to download Adobe Acrobat Reader. Download the reader here

Mr Cheney - who may have to testify at a trial - said he had accepted Mr Libby's resignation with deep regret, adding that he must be presumed innocent until found guilty.

Speaking outside the White House, President George W Bush said Mr Libby had "sacrificed much" and served in "extraordinary times".

He said Mr Libby could expect "due process and a fair trial".

'Lied under oath'

This latest crisis for the Bush administration follows the withdrawal on Thursday of the president's nominee for the Supreme Court, Harriet Miers, after criticism from Mr Bush's conservative supporters.

Patrick Fitzgerald says his inquiry into the leak is not yet over

Meanwhile, Mr Bush's right-hand man, Karl Rove, is still in a state of limbo. His lawyer says he is still under investigation.

The prosecutor, Mr Fitzergerald, said the investigation was not yet over, but he would not speculate on whether anyone else would be charged.

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"At the end of the day, what appears is that Mr Libby's story, that he was at the tail end of a chain of phone calls, passing on from one reporter what he heard from another, was not true - it was false," he said.

"He was at the beginning of the chain of the phone calls, the first official to disclose this information outside the government, to a reporter. And he lied about it afterwards, under oath, and repeatedly."

He said the indictment showed the world that all Americans, no matter what their position, were bound by the law.

The disclosure had not only damaged Ms Plame but also compromised US national security, he said.

Senate Democratic Leader Harry Reid said the bigger picture was "about how the Bush White House manufactured and manipulated intelligence in order to bolster its case for the war in Iraq and to discredit anyone who dared to challenge the president".

Ms Plame's identity was leaked after her husband, diplomat Joseph Wilson, accused the Bush administration of manipulating intelligence to support military action against Iraq.

Mr Wilson says it was done to undermine his credibility. Others have raised the possibility that it was a form of payback for her husband's criticism.