A missile strike apparently targeting al-Qaeda's deputy leader in a village in Pakistan has prompted Islamabad to protest to its American allies.
Ayman al-Zawahiri was not in the village on the border with Afghanistan, Pakistan officials said. But the attack left at least 18 local people dead.
The US military has denied knowledge of the attack, which US media reported had been carried out by the CIA.
But Islamabad condemned the strike and called the US ambassador to complain.
Pakistan's Information Minister Sheikh Rashid Ahmed told a news conference the Pakistani government wanted "to assure the people we will not allow such incidents to reoccur".
He said he did not know whether Zawahiri had been in the area at the time.
Zawahiri has eluded capture since the US overthrew the Taleban in Afghanistan in 2001 despite a $25m bounty on his head.
Osama Bin Laden's second-in-command is regarded as the ideological brains behind the al-Qaeda network, says BBC security correspondent Gordon Corera.
The Egyptian has also become its most visible spokesperson, issuing a number of video and audio tapes, whilst Osama Bin Laden has not been seen or heard from for more than a year.
The raid took place in the village of Damadola in the Bajaur tribal area, about 7km (4.5 miles) from the Afghan border.
Jets - or in some accounts a Predator drone - reportedly fired missiles at a particular housing compound in the village.
Tribesmen there are convinced the strike was the work of the Americans and are very angry at the attack.
Zawahiri has been in hiding since 2001
Reporters who reached Damadola spoke of three houses hundreds of metres apart that had been destroyed.
Shah Zaman said he lost two of his sons and a daughter. "I ran out and saw planes. I ran toward a nearby mountain with my wife. When we were running we heard three more explosions. I saw my home being hit.
"According to preliminary investigations there was foreign presence in the area and that, in all probability, was targeted from across the border in Afghanistan," Pakistan's foreign ministry said in a statement, adding it had complained to the US envoy in Islamabad.
A Pakistani intelligence official told Reuters news agency that Damadola was the stronghold of a banned pro-Taleban group, the Tehrik-e-Nifaz-e-Shariat-e-Mohammadi.
The US has about 20,000 troops in Afghanistan, but Pakistan does not allow them to operate across the border.
Pakistan has about 70,000 troops in the border region.