The United States said Tuesday it was certain a CIA drone strike killed Al-Qaeda number two Abu Yahya al-Libi, claiming its top scalp from the terror group since eliminating Osama bin Laden.

A US official told AFP that Washington had a "high degree of confidence" that Libi was killed in a pre-dawn strike in Pakistan's tribal areas on Monday, part of a intense spate of assaults in the region against the terror group.

"It is significant," the official said, arguing that Libi was in charge of Al-Qaeda operations in Pakistan and outreach to affiliates such as Yemen-based Al-Qaeda in the Arabian Peninsula (AQAP) which has attacked US targets.

News of the killing of Libi followed reports detailing the scope of the US campaign against global terrorism, including revelations that President Barack Obama personally presides over a "kill list" of top suspects.

Libi's death will also bolster Obama's credentials as a steely commander-in-chief as he seeks to repel claims of weakness abroad leveled by his Republican opponent in November's election Mitt Romney.

But it may once again worsen tenuous US ties with nominal anti-terror ally Pakistan, brought almost to the point of rupture by drone strikes, the US raid that killed bin Laden last year and the Pakistani refusal to reopen NATO supply lines into Afghanistan.

Libi was killed in a pre-dawn strike Monday in North Waziristan, a Taliban and Al-Qaeda stronghold along the Afghan border. He was a Libyan citizen with a $1 million price on his head.

A trusted lieutenant of bin Laden, Libi appeared in countless Al-Qaeda videos and was considered the chief architect of its global propaganda machine.

The US official, speaking on condition of anonymity, said that al-Libi had served as the group's "general manager" and had overseen day-to-day operations in Pakistani tribal areas.

The official described the killing of Libi as a "major blow" to Al-Qaeda's core which would further pressure the group's leader Ayman al-Zawahiri

Pakistani officials had originally said it was unclear whether Libi had been present at a compound in the village of Hesokhel, east of Miranshah, the capital of North Waziristan.

Libi had evaded US clutches before: he escaped from a high security US prison at Bagram Air Base in Afghanistan in 2005.

There had also been unconfirmed reports that Libi was wounded in a US drone strike that killed nine militants on May 28. A report that he was killed in a December 2009 drone strike in South Waziristan also proved false.

Libi's death followed the US claim that Atiyah abd al-Rahman, then described in Washington as Al-Qaeda's number two, was killed in a US missile strike in North Waziristan on August 22 last year.

Ben Venzke, an analyst at the US-based IntelCenter, said that the "loss of Abu Yahya al-Libi would be felt throughout the jihadi community as he has been one of the most visible jihadi figures from any of the groups around the world, with prolific video releases and writings."

Documents seized from bin Laden's compound and released by the United States last month suggest Libi was one of the late terror mastermind's most trusted lieutenants.

He signed a letter dated December 3, 2010 and sent to the Pakistani Taliban leader Hakimullah Mehsud reprimanding him for making "legal and religious mistakes" including the mass killing of Muslim civilians in suicide attacks.

Obama has presided over a relentless attempt to crush Al-Qaeda, including in Pakistan and Yemen since taking office in 2009.

Last month, during a visit to Afghanistan, he said his goal of defeating the group behind the September 11 attacks in 2001 was "now within our reach."

[This video grab, released by Al-Qaeda's as-Sahab Media in 2007, shows Abu Yahya al-Libi. AFP Photo]