"A top US congressional Democrat has raised the possibility of George Bush's impeachment in a bid to force him to withdraw troops from Iraq.

Representative John Murtha, chairing the House Subcommittee on Defense which holds the purse strings of the US military, made the comment Sunday in response to repeated threats by the president to veto legislation that calls for withdrawal of US troops from Iraq by the end of next March.

"There's three ways or four ways to influence a president," Murtha said on CBS's "Face the Nation" program. "One is popular opinion; the election; third is impeachment and fourth is, and fourth is the purse."

Asked specifically if Democrats, who now control the US Congress, were seriously contemplating the impeachment option, the congressman, who is close to House Speaker Nancy Pelosi, responded, "What I'm saying, there're four ways to influence a president ... And one of them is impeachment."

Some of the fiercest critics of President Bush have long charged he has illegally manipulated intelligence in order to accuse the Iraqi government of ex-president Saddam Hussein of secretly stockpiling weapons of mass destruction and thus create a pretext for the March 2003 invasion of Iraq.

No weapons of mass destruction have been found in Iraq by US experts, but the White House has strongly denied the intelligence manipulation charge. "