"I do not agree that we have a failed policy," Casey told the Senate Armed Services Committee. "I believe the president's new strategy will enhance the policy we have."

Under the new plan, five army combat brigades and two marine battalions totaling more than 21,500 troops will be added to the 138,000-strong US force in Iraq and put mainly in Baghdad in an attempt to break the cycle of sectarian violence there.

The Congressional Budget Office estimated that as many as 48,000 additional troops will have to be deployed when support troops are taken into account.

Casey, who has been nominated to become the army's chief of staff after two and a half years in Iraq, helped draw up the plan but it will fall to his successor, General David Petraeus, to carry it out.

"I do believe the job in Baghdad as it's designed now can be done with less than that. But having the other three brigades on a deployment cycle gives General Petraeus great flexibility," he said.

"It allows him to make assessments on whether the plan is working or not and to either reinforce success, maintain momentum or put more forces where the plan is not working," he said.

Casey said he had brought in more US troops at various points since taking over command in Iraq in July 2004, but his "general view" was that more US forces prevents Iraqi security forces from assuming responsibility for their own country.

"My general belief is I did not want to bring one more soldier into Iraq than was necessary to accomplish the mission," he said. "And so what I asked for was the two brigades and the ability to maintain a reserve in Kuwait in case I needed additional flexibility."

Casey faced a barrage of biting questions from Senator John McCain who questioned his judgement and cited the general's past prediction that his strategy would allow a drawdown in US forces by late 2005.

"And we have paid a very, very heavy price in American blood and treasure because of what is now agreed to by literally everyone as a failed policy," McCain said.

Casey's strategy of training and equipping Iraqi security forces to assume control over the country came under attack from other senators on both sides of the aisle as a failure.

The general made no attempt to duck responsibility for the military strategy, saying he had been given the troops he had asked for and the strategy was his.

"I'm responsible for military aspects to this campaign and to the extent people have problems with the way that's been conducted, then I am the one who's responsible," he said.

Casey acknowledged the situation in central Iraq, and particularly Baghdad, is bad.

He said Iraqi security forces had proved unreliable and unable to hold areas cleared by US forces in Baghdad last year in an earlier campaign to secure the city.

Two US brigades were put into the city in June as the security plan faltered, including a Stryker brigade whose year-long tour of duty was extended.

But the government of Prime Minister Nuri al-Maliki would not commit to a policy of targeting anyone who was breaking the law, no safe havens and no political interference in the security forces, he said.

"And I was reluctant throughout the fall to ask for additional forces ... when I knew I didn't have the political commitment from the Iraqis to allow us to do our jobs," Casey said.

According to the US administration, Maliki has since made those political commitments as part of the revised strategy, and Casey said he has delivered on them so far.

In Iraq on Thursday, at least 70 people were killed in suicide and car bombings, while security officials said bitter sectarian attacks had claimed the lives of nearly 2,000 civilians throughout the country in January.

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