It is not yet clear whether the deadly airstrike aimed at al-Qaeda's deputy leader, which killed 18 people, hit its target, the Washington Post said yesterday.
In Pakistan, officials said earlier indications from US intelligence sources that a key lieutenant of Osama bin Laden, possibly his No. 2 Ayman al-Zawahiri, may have died in Friday's missile raid were "not true."
Yet "in Washington, US intelligence sources said it was too early to know whether the strike had killed Zawahiri, 54, an Egyptian physician who is al-Qaeda leader Osama bin Laden's top aide," the Post said.
The paper quoted an unidentified source as saying: "The outcome of this doesn't seem decided."
In addition, "US officials defended the strike, saying it was the right course of action based on timely intelligence about Zawahiri's whereabouts early Friday. Zawahiri had been under surveillance by the CIA for two weeks, security sources said," according to the Post.
"US military sources said Pakistan's intelligence service had been heavily involved in the attack," the Post said, adding: "Senior Pakistani officials would not confirm involvement in the strike but acknowledged regular intelligence cooperation with the United States."
"The intelligence sharing is on an almost daily basis," the Post quoted a senior Pakistani intelligence official as saying.
The official said the cooperation included sharing of both human and electronic intelligence sources, the Post said.
Pakistan's foreign ministry said it had summoned US ambassador Ryan Crocker on Saturday and handed over a formal protest about the incident.
The US Defense Department denied that the US military had carried out any attacks in the area.
Pakistan forbids military operations by foreign forces in its territory.
But CIA sources said on Saturday that they had unconfirmed indications that a key target -- possibly bin Laden's Egyptian deputy and chief ideologue -- had died in a raid by a US Predator drone in Pakistan.
Citing US defense sources, US television network NBC said the strike had targeted the 55-year-old Zawahiri.
But senior Pakistani government and intelligence officials said Zawahiri was thought not to have been in the area at the time of the air strike.
The CIA is known to conduct operations along the Afghan border in the hunt for bin Laden and his deputies.
They are thought to have fled Afghanistan when US-led forces overthrew the hardline Taliban regime in late 2001.