United States intelligence analysts are not convinced by the evidence offered so far by Pakistani authorities that Baitullah Mehsud, a Taliban leader linked to Al Qaeda, was responsible for former prime minister Benazir Bhutto's assassination, officials in New York said.

Pakistani authorities, working from a single intelligence intercept they collected the day after Bhutto's death, in which Mehsud is said to be congratulating a man on a 'sepactacular job', have identified the militant leader as the chief suspect behind the attack.

But the New York Times quoted an unidentified senior state department official as saying that they needed more evidence. "The Pakistanis are saying this is it, this is the proof," the official said. "Before our guys say yes or no, they need a hell of a lot more than one thing, even if it is a substantial piece of evidence," he told the paper.

Pentagon officials said that American analysts were examining several other potential enemies of Bhutto, including elements of Pakistani Taliban groups and other Islamic extremists.

"There are so many people who'd want to kill her, it's difficult to ascribe any one agency," the official said.

Based in the south Waziristan tribal areas near the Afghan border, Mehsud has been accused by Pakistani officials of being behind most of the suicide attacks on government, military and intelligence targets in recent months.

American officials were also quoted as saying that the United States did not have access to all the information available to Pakistani authorities, and that in the end, Mehsud might well be held responsible for the attack on Bhutto.