Pakistan's top security officials on Wednesday were searching for clues that a "moderately important terrorist target" may have been hit when U.S. and/or NATO forces attacked three houses in a remote part of the country's border region with Afghanistan.
As many as 15 people were killed in the early morning strike Wednesday.
The operation took place near the village of Angor Adda in Pakistan's South Waziristan region - a notorious sanctuary for al Qaeda and Taliban militants. Eyewitnesses said the strike involved helicopter gunships.
South Waziristan and the adjoining North Waziristan regions are known to harbor fighters who routinely cross the border into Afghanistan to attack U.S. and other Western troops then return to the relative security of Pakistani soil.
Wednesday's attack was unusual in that it involved Western ground forces, a Pakistani security official told CBS News on condition of anonymity.
Previous attacks on the Pakistani side of the border are believed to have been carried out primarily by CIA pilotless drones armed with hellfire missiles.
An official at the U.S. Military command center in Bagram, Afghanistan, told CBS Wednesday that he could neither confirm nor deny any American operation in South Waziristan. "I've got nothing for you," the spokesman said.
The reported use of ground troops prompted speculation that the attack was aimed at an important terrorist target, but also enraged local residents and authorities, who have long insisted that Western forces must not enter Pakistani territory.
"I don't know if there were any top targets. But there could well be moderately important terrorist targets," the security official told CBS. "If there was deployment of grounds troops, which involved a greater risk than sending in a pilotless drone, that suggests the attackers were probably looking for a specific terrorist target."
In Islamabad, a senior European diplomat from a NATO member country said initial information led him to believe the attack was carried out by a joint team of U.S. Special Forces and NATO troops based in Afghanistan, thought he could not immediately confirm the presence of ground forces.
The diplomat, who also spoke to CBS on condition of anonymity, said "the use of ground troops must be to either capture or kidnap someone important."
Meanwhile, there were conflicting reports Wednesday about whether Pakistani Prime Minister Yusuf Raza Gilani had survived an assassination attempt when shots were fired at his motorcade near Islamabad's international airport. (.)
An eyewitness from the village that was struck in South Waziristan said nine people were killed in one house - all of them locals with no ties to militants, including at least five women and children.
Khan Gul Wazir told CBS News by telephone on Wednesday that he had been awake for early morning prayers when he heard loud gunfire and explosions. He said he ran outside and saw smoke pouring from one of his neighbor's homes.
Wazir said he saw American troops surrounding the house and blocking off the area. He also reported five U.S. helicopters hovering over the area for the duration of the operation, which he said lasted one hour.
A spokesman for the Governor of Pakistan's Northwest Frontier Province, who also officially administers the North and South Waziristan, told CBS that 20 people had been killed in the raid, including women and children. His office officially condemned the attack as a violation of Pakistan's territorial sovereignty.
Asked if he could confirm the presence of American soldiers Wednesday, Pakistani Army spokesman Major Murad told CBS they aware of attack, but not yet sure who had carried it out.
"We are investigating and soon we will issue a proper statement," said Murad.
Wazir told CBS that in addition to the house where nine people were killed, two other nearby homes were hit in the village, which sits close to the border with Afghanistan. He said he saw the bodies of no "strangers" among the dead.
A local tribal elder who acts as a go-between for the community and the government said the villages in the area are often subjected to violence because militants use peoples' homes to take shelter after crossing border, with or without their consent.
Wazir said the situation for he and his neighbors had grown far worse since President Pervez Musharraf's decision to resign under huge domestic pressure about two weeks ago.
A Taliban militant from the area told CBS News that Wednesday's was not the first such ground operation. He said three weeks ago U.S. helicopters landed in a village, kidnapped one person from a house and injured an old man inside. The militant also said the number of U.S. aircraft - mostly the pilotless drones - flying over North and South Waziristan had increased "300 percent" during the past month.
The CIA and other Western intelligence agencies are known to have scrutinized intelligence coming from North and South Waziristan in the past in their searched for some of al Qaeda's top leaders; most notably Osama bin Laden and his deputy Ayman al-Zawahri.
The Pakistani security official who spoke to CBS News said Pakistani military and intelligence forces in the region had also carried out an intense search for al Qaeda's leaders as recently as last month, based on "information which provided to us with some new clues."
The Pakistani official refused to elaborate on the nature of that information but said "the situation in Waziristan remains of immense interest to all of us."