An Al Qaeda [Images] leader based in Afghanistan has claimed responsibility for the assassination of former Pakistan Premier Benazir Bhutto [Images], whom he described as 'the most precious American asset.'

"We terminated the most precious American asset, which vowed to defeat (the) mujahadeen," Al Qaeda commander and spokesman Mustafa Abu Al-Yazid told Italian news agency Adnkronos International in a phone call from an unknown location.

Al-Yazid was described by AKI as the 'main Al Qaeda commander in Afghanistan.' It reported that the decision to kill Bhutto was made by Al Qaeda second-in-command Ayman al-Zawahiri in October.

The report said death squads were allegedly constituted for the mission and that a cell comprising a 'Punjabi volunteer' of the Lashkar-i-Jhangvi carried out Bhutto's assassination.

Bhutto died after being shot by a suicide attacker, who later blew himself up near her convoy of armoured vehicles just after she addressed an election rally at Rawalpindi. The blast killed about 20 people.

During her campaign to drum up support for her Pakistan People's Party, Bhutto had repeatedly attacked elements that were fomenting extremism and militancy in northwestern region of the country and vowed to crack down on militant groups.

Bhutto, who returned to Pakistan from exile two months ago, had earlier survived a suicide attack on her homecoming procession in Karachi on October 18 that killed 140 people and injured hundreds more.

Baitullah Mehsud, a militant leader who was recently made head of Tekrik Taliban-e-Pakistan -- a coalition of Pakistani Taliban groups, had reportedly issued threats that he would send suicide bombers to target Bhutto.