Suspected US spy drones fired missiles early on Thursday into a Pakistani tribal area seen as a safe haven for Al-Qaeda and Taliban militants, killing six people, security officials said.
The incident in the lawless district of North Waziristan on the border with Afghanistan was the latest in a string of attacks on Pakistani soil that have raised tensions between Islamabad and Washington.
The missiles hit a madrassa, or an Islamic religious school, in a village just outside Miranshah, the main town in the tribal area, residents and officials said.
"At 2:25 am, two spy drones fired three missiles at the madrassa of Mullah Mansoor. Three people were killed immediately, four were injured and another later expired at hospital," a security official told AFP.
Another security official and a witness later put the death toll at six, saying tribesmen clearing the rubble at the site of the attack has found remains of two other people.
Residents said that all of the victims were local tribesmen, adding that locals had fired at two suspected US drones hovering above.
There was no immediate confirmation of the strike from the Pakistani military or from the US-led coalition in Afghanistan.
The strike came hours after Pakistani lawmakers passed a unanimous resolution during a closed-doors joint session of parliament demanding that the government do more to put an end to US military action on Pakistani soil.
"The nation stands united against any incursions and invasions of the homeland, and calls upon the government to deal with it effectively," the resolution said.
Missile strikes targeting militants in Pakistan in recent weeks have been blamed on US-led coalition forces or CIA drones based in Afghanistan.
The United States has stepped up attacks on militants in Pakistani territory since a new civilian government came to power in Islamabad in March.
Five people were killed in a similar strike last week in South Waziristan, which is a stronghold of Pakistani Taliban chief Baitullah Mehsud.
Mehsud, the head of the umbrella Taliban organisation Tehreek-e-Taliban Pakistan (TTP), was accused by Islamabad and the United States of masterminding the killing of former premier Benazir Bhutto in December 2007.
Relations have also been strained by a raid by US special operations forces into Pakistan on September 3 which killed several Pakistanis.
Pakistani President Asif Ali Zardari has vowed zero tolerance against violations of his country's sovereignty amid the strikes, which have stoked anti-US sentiment in Pakistan.
US and Afghan officials say northwest Pakistan is a safe haven for Al-Qaeda and Taliban militants who sneaked in from Afghanistan after the fall of the Taliban regime in late 2001.
Al-Qaeda chief Osama bin Laden and his deputy, Ayman al-Zawahiri, are widely believed to be hiding in the area.