The U.S. intelligence agencies were still investigating whether al-Qaeda terrorists had been behind the assassination of Pakistan's former Prime Minister Benazir Bhutto , the White House said on Friday.

"There have been many claims of responsibility. Our intelligence community is still looking into it," White House spokesman Scott Stanzel told reporters at Crawford, Texas, where President George W. Bush's family is spending their New Year holiday.

Pakistan Interior Ministry spokesman Javed Iqbal Cheema told a news conference on Friday that they have intercepted intelligence indicating Baitullah Mehsud, al-Qaeda leader based in the South Waziristan region on the Afghan border, was behind the killing of Bhutto .

Bhutto, 54, was killed in a suicide bombing on Thursday when she was leaving an election rally in Rawalpindi. More than 20 others also died and nearly 60 were injured in the attack.

She served twice as Pakistan's prime minister between 1988 and 1996. After living in exile for 8 years, she returned to Pakistan on Oct. 18. A suicide attack at her homecoming parade in Karachi took more than 140 lives.

Stanzel said on Thursday that the suicide bombing employed to assassinate Bhutto was an al-Qaeda tactic.

"Whoever perpetrated this attack is an enemy of democracy and has used a tactic which Al-Qaeda is very familiar with, and that is suicide bombing and the taking of innocent lives to try to disrupt a democratic process," he added.

(Xinhua News Agency December 29, 2007)