Lewis 'Scooter' Libby, US vice president Dick Cheney's closest aide, resigned tonight after being charged with perjury over the leaking of the name of an undercover CIA agent.

Mr Libby has also been charged with the obstruction of justice and making false statements to a grand jury, following a two-year investigation led by Special Prosecutor Patrick Fitzgerald.

He has become the first senior White House official to be indicted in more than a century, and faces a maximum sentence of 30 years in prison or a $1.25 million fine.

Karl Rove, President Bush's chief political strategist, was not charged today but has not been cleared. He remains under investigation.

Vice President Dick Cheney said tonight that his former chief of staff was presumed innocent until a contrary finding is made by a jury.

In a written statement, Mr Cheney said he had accepted Mr Libby's resignation with deep regret. “In our system of government an accused person is presumed innocent until a contrary finding is made by a jury after an opportunity to answer the charges and a full airing of the facts. Mr. Libby is entitled to that opportunity,” his statement said.

The charges against him allege that Mr Libby lied to FBI agents who interviewed him on October 14 and November 26, 2003; committed perjury while testifying under oath before the grand jury on March 5 and March 24, 2004; and engaged in obstruction of justice by impeding the grand jury’s investigation into the leaking of Valerie Plame’s affiliation with the CIA to various reporters in the spring of 2003.

In the part that spells the most trouble for the White House, Mr Libby, 55, is accused of lying when he told investigators that he learned about Ms Plame’s CIA status from an NBC journalist. Instead, he learned it from Mr Cheney, the indictment says, thrusting the Vice-President to the heart of the scandal.

In a news conference special prosecutor Patrick Fitzgerald said: "Libby lied repeatedly under oath." He added that the inquiry was substantially complete, but added: “it’s not over.”

He said Valerie Plame’s role in the CIA was unknown by friends and neighbours until her cover was blown in July 2003. The first reporter to be told of her identity was Judith Miller of the New York Times, who spoke to Libby on the subject in June 2003. An investigation was launched that October, when Mr Fitzgerald said Libby had given the FBI a “compelling story” of just “passing gossip from one reporter to another.”

The White House aide allegedly said he had heard about Plame from a journalist via a long chain of phone calls. Libby admitted passing on the information but said he had made it clear that he did not know whether it was true.

Mr Fitzgerald said that according to the indictment the story was fabricated and a “very, very serious matter.” He said Libby had in fact heard about Plame through three different Government officials, including Mr Cheney, weeks earlier.

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