The U.S. Vice-President, Dick Cheney, is expected to come under more pressure over his role in Valerie Plame's case, the former CIA agent, when she testifies before the Congress this week.

It was Plame's exposure that led to the conviction of Cheney's top aide, Lewis “Scooter” Libby for lying and obstruction of justice. Plame's identity was exposed after her husband Joseph Wilson accused the White House of manipulating prewar intelligence over the supposed sale of yellowcake uranium ore to Iraq.

Patrick Fitzgerald, the special prosecutor, said that there was “a cloud over the vice-president”.

Plame is bringing a civil case against Cheney and Karl Rove, another Presidential aide, and other officials for revealing her identity. It is a crime to leak the name of a covert CIA agent, although Plame's precise status has never been revealed.

“This case doesn't end with Mr. Libby's conviction,” said Maurice Hinchey, a Democratic congressman. “Testimony in the Libby trial made it even more obvious that Vice-President Dick Cheney played a major role in Mrs. Wilson's outing.”

Denis Collins, a juror, said about his disappointment last week that the vice-president had not been called to testify: “We didn't know what he might reveal. But figuratively he was the last of the seven veils and we would have liked to have a good look.”

Cheney has gone from being a highly regarded asset to Bush on his election in 2000 to being perceived as one of his biggest liabilities. His influence on foreign policy is on the wane as Condoleezza Rice has quietly redirected Cheney's stance towards negotiations with states such as North Korea and Iran.

Henry Waxman, the Democratic chairman of the government reform committee, is determined to investigate contracts in Iraq awarded to Halliburton, Cheney's old firm, as well as the Plame controversy.

SS/KB