"The failure to finish the job represents a lost kill Osama opportunity that forever altered the course of the conflict in Afghanistan and the future of international terrorism."

Troop decision

The report comes just days before Barack Obama, the US president, is due to announce his decision on whether tens of thousands more troops will be sent to Afghanistan in an attempt to quell resurgent Taliban forces.

in depth

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Eight years on from the 2001 invasion that forced the Taliban from power, up to 35,000 extra US troops are likely to ordered to Afghanistan to "finish the job".

The committee's report criticises Donald Rumsfeld, the then-US defence secretary, and General Tommy Franks, the US general who commanded the invasion of Afghanistan, for not sending more US troops to Tora Bora to block the mountain paths to Pakistan, which were bin Laden's only means of escape.

Fewer than 100 commandoes were on the scene with their Afghan allies and their calls for reinforcements to launch an assault were rejected, the report said.

"The vast array of American military power, from sniper teams to the most mobile divisions of the Marine Corps and the army, was kept on the sidelines," it said.

"Instead, the US command chose to rely on airstrikes and untrained Afghan militias to attack bin laden and on Pakistan's loosely organised Frontier Corps to seal his escape routes."

Bin Laden 'unmolested'

Bin Laden was apparently convinced that the sustained bombardment of the mountains, where he was believed to be hiding with about 100 followers, with up to 100 air raids a day would leave him dead.

On December 14, 2001, he wrote a will, the reports says, instructing his wives not to remarry and apologising to his children for devoting himself to jihad.

But just days later he was able to walk "unmolested" out of Afghan territory into Pakistan's tribal areas, where he is widely believed to still be living.

Rumsfeld had expressed concerns at the time that ordering many more troops into the area to hunt Bin laden would create an anti-American backlash and fuel support for al-Qaeda and the Taliban.

The report was based on reviews of existing literature, unclassified government records and interviews with participants.

Staff members for the Senate Foreign Relations Committee's Democratic majority prepared the report at the request of the chairman, Senator John Kerry.

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