Washington, June 30: US President Barack Obama's counter-terrorism advisor, John Brennan, has revealed new details about Osama bin Laden and how the Al-Qaeda leader had spent the last six years of his life in a residential compound in Pakistan before being killed in a US military operation last month.

"He practiced absolutely phenomenal operational security. To our knowledge, he never left that compound once he got there. Of the [other] people there, most never left either," the Washington Post quoted Brennan, as saying.

"We don't know how many people in Al-Qaeda's senior leadership knew where bin Laden was. He was confident and relaxed. We think he was totally taken by surprise," he added.

Brennan further echoed other senior US officials in saying that "the Pakistani leadership - military, political, intelligence - was caught totally unawares by the fact that bin Laden was found in a compound in Abbottabad".

He acknowledged that the US relationship with Pakistan "is not without tension or frustration," but said that continued cooperation is "essential."

"Pakistan has been critical to many of our most significant successes against Al-Qaeda. Tens of thousands of Pakistanis - military and civilian - have given their lives in the fight against militancy. And despite recent tensions, I am confident that Pakistan will remain one of our most important counter-terrorism partners," Brennan said.

Bin Laden, who had evaded capture for a decade, was killed in a top secret operation involving a small team of US Special Forces in Abbottabad on May 2.

The Saudi-born terrorist, accused of being behind a number of atrocities, including the attacks on New York and Washington on 11 September 2001, was at the top of the US "most wanted" list. (ANI)