President Bush’s controversial plans to send tens of thousands more US troops to Iraq are being resisted by leading figures at the Pentagon.

The Joint Chiefs of Staff, the US military’s most senior generals, are concerned that such a short-term surge in the US presence would further fuel the fighting by armed factions in Iraq rather than pacify the country.

Their misgivings come as the Pentagon reported yesterday that violence in Iraq had reached unprecedented levels.

The Pentagon’s most pessimistic report yet on Iraq states that violent attacks are now at record highs of 959 a week; that Shia death squads have eclipsed al-Qaeda as the most lethal and destabilising force in the country; and that insurgent efforts to undermine the Iraqi Government are succeeding.

But the most significant conclusion is that the large military operation begun in August by American and Iraqi forces to stabilise Baghdad — a move that included beefing up US troop levels in the capital — has utterly failed.

Mr Bush is expected to lay out his new thinking on Iraq in the new year, and officials have indicated that he is likely to order in up to 50,000 more US troops.

The Pentagon report, analysing the situation in Iraq between August and November, stated that there were 1,028 sectarian killings in October. In January, before the February 22 bombing of the Shia al-Askariya mosque that unleashed this year’s sectarian carnage, there were 180 killings. “The violence has escalated at an unbelievably rapid pace,” Marine Lieutenant General John P. Sattler, of the US Marines, who briefed journalists on the report, said.

General Sattler appeared to imply that no amount of extra troops could quell the violence. “I don’t know how many forces you could push into a country . . . that could cover the entire country, where these death squads wouldn’t find somebody.”

The Pentagon report states for the first time that al-Mahdi Army, the militia controlled by the Shia cleric Hojatoleslam Moqtada al-Sadr, has replaced al-Qaeda as the “most dangerous force” in the country.

General James Conway, the head of the Marines, said on Saturday that the Joint Chiefs would support a troop increase only if there was a “solid military reason” for doing so. “But I can tell you, we do not believe that adding numbers just for the sake of adding numbers, just to be thickening the mix, is the way to go.”

Mr Bush, in an interview in today’s Washington Post, said that he was addressing a major concern of the Joint Chiefs that the US military was stretched too thin worldwide. He said that he had instructed Robert Gates, the new Defence Secretary, to give him a plan to substantially increase the Army and Marines for the long-term fight against terrorism. Mr Gates will travel to Iraq soon and will be a key player in what decision is made.

Colin Powell, Mr Bush’s former Secretary of State and Chairman of the Joint Chiefs during the first Gulf War, said on Sunday that the US was losing in Iraq, that he opposed a troop increase, and that a troop reduction should begin in mid-2007.

• Hillary Clinton for the first time yesterday disavowed her vote in 2002 authorising the invasion of Iraq and said that she would announce in the new year if she would run for the presidency (Tim Reid writes).

  “I take responsibility for that vote,” Mrs Clinton told NBC. “Obviously, if we knew then what we know now, there wouldn’t have been a [senate] vote and I certainly wouldn’t have voted that way.”

  Mrs Clinton said that she was disinclined to support an increase in troops to Iraq, even short-term. “I’m not going to believe this President again,” she said.

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