Washington: The US President Barack Obama has declared that America had "cut off" al-Qaeda's head with the killing of its chief and would ultimately crush the terror outfit.

"We have cut off their head and we will ultimately defeat them," he said on Friday evening after meeting privately with members of the assault team that killed bin Laden in the Pakistani garrison city of Abbottabad on Monday.

"We're making progress in our major goal, our central goal in Pakistan and Afghanistan, and that is disrupting and dismantling and ... ultimately defeating al-Qaeda," Obama said at Fort Campbell, Kentucky, where had gone to address American troops on their return from active duty in Afghanistan.

After the announcement of Laden killing on Monday in a successful US operation in the Pakistani garrison city of Abbottabad, it was the President's first major address on the issue.

Salute for ‘job well done’

Obama also met the American special forces commandos, who killed bin Laden, and saluted them on behalf of the US and people all over the world for a "job well done".

Obama awarded a Presidential Unit Citation - the highest such honour that can be given to a unit - to those involved in the operation in recognition of their extraordinary service and achievement.

"Here at Fort Campbell, I had the privilege of meeting the extraordinary Special Ops folks who honored that promise. It was a chance for me to say on behalf of all Americans and
people around the world, job well done. Job well done," Obama said later in his address to the troops.

The President, who was accompanied by Vice President Joe Biden, was briefed about the operation by members of the special operations troops who executed the dangerous raid on
bin Laden's compound in Abbottabad.

The President and Vice President also met the 160th Special Operations Aviation Regiment and the 5th Special Forces Group to thank them for their service.

"Thanks to the incredible skill and courage of countless individuals -— intelligence, military —- over many years, the terrorist leader who struck our nation on 9/11 will never threaten America again," Obama said.

Tough fight continues

At the same time, Obama conceded that this continues to be a very tough fight.

"You know that. But because of this progress, we're moving into a new phase. In the coming months, we'll start transferring responsibility for security to Afghan forces.

"Starting this summer, we'll begin reducing American forces. As we transition, we'll build a long-term partnership with the Afghan people, so that al-Qaeda can never again threaten America from that country," he said.

US Army most capable

Terming US Army as the most capable force in the world, Biden said, “Let me say this without any fear of contradiction, you're the most capable warriors in the history of the world. There has never, never, never, never been a fighting force as capable as you are.”

Meanwhile, Defence Secretary Robert Gates said the killing of bin Laden could be "a game changer" in the war against terrorism.

"In terms of the impact of the killing of Osama bin Laden, in terms of the situation in Afghanistan, I think that there is a possibility that it could be a game changer," Gates said in response to a question during a troop visit at Seymour Johnson Air Force Base.

Observing that bin Laden and Taliban leader Mullah Omar shared a very close personal relationship, Gates, however, said there are others in the Taliban who have felt betrayed by al-Qaeda, that it was because of al-Qaeda's attack on the US that the Taliban got thrown out of Afghanistan.