Islamabad: Pakistan's Interior Minister Rehman Malik said on Sunday that he was "98 per cent sure" senior al Qaeda figure Ilyas Kashmiri had been killed in a US drone strike near the Afghan border.
US officials in Washington said however they were highly sceptical of reports that Kashmiri, seen by them as one of the world's most dangerous militants, was dead.
"All ground intelligence shows that he is dead. What I can say is there is a 98 per cent chance he is dead," Interior Minister Rehman Malik told Reuters.
US officials said they were highly sceptical of reports that Kashmiri was dead.
"Since we do not have the body. We do not have DNA we need to confirm. This is the substantive evidence we are looking for."
It is very difficult for Pakistani security forces to operate in areas like South Waziristan, where intelligence officials said Kashmiri was killed by a drone on Friday night.
After missile strikes by the remotely-operated aircraft, militants often seal off the area then bury their comrades.
Kashmiri was said to have been killed in a part of South Waziristan controlled by senior Taliban commander Maulvi Nazir. Siddiqullah, one of Nazir's commanders, said Kashmiri was dead.
"I confirm the commander Ilyas Kashmiri was martyred. We have buried his body in Lamand," Sidiqullah told Reuters by telephone from an undisclosed location.
"Pakistan's government is just as responsible for the martyrdom of commander Ilyas as the United States and Western powers. We will take revenge against the Pakistani government" he added.
A senior Pakistani security official said, "It's almost confirmed that he is dead. Different sources confirmed it but we can't say it is 100 per cent confirmed because we don't have the body."
He went on to say that Kashmiri had been holding a meeting with other militants when the drone missile struck.
In Washington, there was scepticism. One US National Security official told Reuters it was more likely than not that Kashmiri was still alive, and another said he believed he had not been killed.
The elimination of Kashmiri would be another coup for the United States after American special forces killed Osama bin Laden in a garrison town close to Islamabad on May 2.
But the killing of bin Laden aroused international suspicions that Pakistani authorities had been complicit in hiding him, and led to domestic criticism of them for failing to detect or stop the US team that killed him.
US doubts over Kashmiri's reported demise may reflect the deep distrust between Pakistani and US intelligence services.
A Pakistani intelligence official said Pakistan had tipped off the Americans about the whereabouts of Kashmiri, whom the US Department of State has labelled a "specially designated global terrorist".
Kashmiri, said to be a former Pakistani military officer, has been linked to attacks including the 2008 rampage through the Indian city of Mumbai which killed 166 people.
A Pakistani television station quoted the group Kashmiri headed, Harkat-ul Jihad Islami (HUJI) which is allied to al Qaeda, as saying he has dead and that it would avenge him.
The SITE online monitoring service said the HUJI statement was posted on a jihadist forum it tracks. A US National Security official expressed doubts about the statement. Its authenticity could not be independently verified.
Kashmiri was reported to have been killed in a September 2009 strike by a US drone. But he resurfaced and gave an interview to Asia Times online correspondent Saleem Shahzad.
Shahzad disappeared from Islamabad a week ago. His body was found in a canal two days later with what police said were torture marks. The media and human rights groups have speculated that Pakistan's military intelligence agency may have had a hand in the killing, an allegation it strongly denied.
Human Rights Watch said Shahzad had voiced concern about his safety after getting threatening telephone calls from Pakistani intelligence agents and had been under surveillance since 2010.
Before his death, Shahzad wrote an article stating that Kashmiri's followers carried out an attack on the PNS Mehran naval base in Karachi in May which drew sharp public criticism of the Pakistani military.