US defence secretary Leon Panetta on Thursday said the daring operation to kill Osama bin Laden at his Abbottabad safe house was very risky as the al-Qaeda chief's presence there was not 100% confirmed. As Director of the CIA, Panetta played a leading role in the finding and killing of bin Laden. Subsequently he was made the defense secretary by President Barack Obama.

"What I saw was a very professional intelligence operation that was able to determine the location of the compound in Abbottabad," Panetta told reporters in his final press conference as the defense secretary.

If confirmed by the Senate, he would be replaced by Chuck Hagel, the former Nebraska Senator.

"I think despite all of the work that was done on the intelligence side we were putting the bits and pieces together, we never had a hundred per cent confidence that it was bin Laden who was located there. So from the very beginning, it was always very risky because we didn't know that in fact it was bin Laden," he said.

"We continued to look at the intelligence. It seemed to all point to it being bin Laden, but very frankly, we did not have a hundred percent," he said.

Panetta disclosed that during planning for the operation, there were a lot of different views that raised questions and concerns about whether or not the US should do this.

"I remained very confident that, with the information we had, the best information we'd had on bin Laden since Tora Bora, that it was important for us not to simply ignore what we had but to take action and to go in and determine whether or not it was him," Panetta said.