The Bush administration faced rising doubts about its Iraq policy following weeks of deadly violence across the country, three years after the March 2003 US-led invasion to remove Saddam Hussein from power.

Thousand of anti-war protesters demonstrate Sunday, March 19, 2006, in Portland, Ore. It was a weekend of protests in Oregon and across the nation against the war in Iraq. [AP]

US opinion polls this week showed support among Americans for Bush and the war had plunged to new lows.

On Friday Newsweek magazine's newest poll showed that approval of Bush's handling of Iraq had plummeted to 29 percent while those who disapprove of his Iraq policy shot up to 65 percent.

A Wall Street Journal/NBC News poll Thursday put Bush's overall approval ratings at 37 percent.

With political party and faction leaders in Baghdad deadlocked over forming a national government, top US senators called on Bush to put greater pressure on them.

Hagel, who said the country had been in a "low-grade" civil war for as long as a year, added that the United States has to stop talking about "victory" and think through responses to a worst-case scenario, like all-out civil war.

"Are we better off today than we were three years ago? Is the Middle East more stable than it was three years ago? Absolutely not," Hagel told ABC.

"We've got to think in a big-picture way here that we haven't thought before," he said, mentioning talking more with Iraq's neighbors including Iran.

Also on ABC, Democratic Senator Jack Reed said that the United States needs to threaten Iraq's leaders with the pullout of US troops if they cannot come to an accord over governing the war-riven country.

"I think we have to make it clear to the Iraqi political leaders that if they're not able or willing to come together with a political solution that recognizes the differences and pulls together different factions, that our presence can't be indefinite there," Reed said.

Democratic Representative John Murtha, a retired Marine colonel, called on the White House to withdraw troops from Iraq, which "is already a civil war".

"We could do it in six months," he told NBC's "Meet the Press."

"And I think we'd be better off. The troops would be better off. The country would be better off."