Osama bin Laden bemoaned "disaster after disaster" inflicted by the US onslaught on Al-Qaeda before he was killed and even mulled changing his terror group's name, a top US official said Monday.

On the eve of the anniversary of bin Laden's death, President Barack Obama's top counter-terrorism aide John Brennan argued that a US drone campaign had left Al-Qaeda seriously weakened, and unable to replace wiped-out leaders.

Brennan said in a speech in Washington that the terror group was losing "badly," was a "shadow" of its former self, and that its core leadership would soon be "no longer relevant."

He said the Al-Qaeda leader's frustration at the demise of his group, which was behind the September 11 attacks in 2001, poured out in documents seized from his compound by US Navy SEAL commandos who killed him a year ago.

"He confessed to 'disaster after disaster'" for Al-Qaeda, Brennan said, noting that some of the captured material would be published online this week by the Combating Terrorism Center at the US Military Academy at West Point.

Brennan also said that subsequent US operations to wipe out senior Al-Qaeda leaders in Pakistan had left the group reeling.

"Under intense pressure in the tribal regions of Pakistan, they have fewer places to train and groom the next generation of operatives, they're struggling to attract new recruits.

"Morale is low," Brennan said in a speech at the Woodrow Wilson Center for International Scholars, which was briefly interrupted by a Code Pink anti-war demonstrator who was hauled out of the room by a burly policeman.

Brennan said that the documents gathered at bin Laden's lair in Abbottabad, outside Islamabad, show the late Al-Qaeda leader urged subordinates to flee for places "away from aircraft photography and bombardment."

Things got so bad for the group which plotted the September 11 attacks in 2001, the deadliest terror strike in US history, that bin Laden considered changing the group's name in a rebranding effort, he said.

Brennan's speech prompted new claims by Republicans that the Obama campaign is exploiting the anniversary of the bin Laden raid to boost the president's prospects of reelection in November.

Senior Obama aides are clearly using the president's decision to launch the high-risk raid as an implicit comparison to the character of his presumptive Republican rival Mitt Romney.

The president himself implicitly suggested in a news conference on Monday that Romney might not have ordered the high-stakes raid last year.

Brennan also claimed that the administration's tactics against Al-Qaeda had made it harder than ever for Al-Qaeda to plan and execute large-scale, potentially catastrophic attacks.

"Today, it is increasingly clear that compared to 9/11, the core Al-Qaeda leadership is a shadow of its former self," Brennan said.

"Al-Qaeda has been left with just a handful of capable leaders and operatives, and with continued pressure is on the path to its destruction.

"And for the first time since this fight began, we can look ahead and envision a world in which the Al-Qaeda core is simply no longer relevant."

Brennan's speech amounted to the administration's most comprehensive public survey about the state of the struggle against Al-Qaeda.

He spent considerable time defending strikes by unmanned US aerial drones in nations like Pakistan, crediting them with dismantling Al-Qaeda's top leadership and causing bin Laden's distress.

Brennan said the strikes were legal, ethical and proportional, and added that Obama had instructed officials to share more details about the secret war.

Despite lauding the administration's achievements in hammering top Al-Qaeda leaders and the group's capacity, Brennan also warned that global terror threats were still potent, particularly those emanating from Africa.

"As the Al-Qaeda core falters, it continues to look to its affiliates and adherents to carry on its murderous cause," Brennan said, warning that the group's merger with the Shebab group in Somalia was "worrying."

He said that Yemen-based Al-Qaeda in the Arabian Peninsula (AQAP) remained a threat, despite the strike that took out radical US-born cleric Anwar al-Awlaki, who directed its external operations.