At least 20 people were killed and 25 others were wounded in a major US aerial attack on Monday in Pakistan’s restive North Waziristan tribal district near the Afghan border, officials said.

Missile-armed Predator drones targeted houses and a seminary linked to Afghan Taliban commander Jalaluddin Haqqani in Dandai Darpakhel village, located on the outskirts of the district's main town of Miranshah.

"Two pilotless aircraft fired at least four missiles at around 9:30 am (0330 GMT) killing up to 20 people, most of them were women and children," said Sanaullah Khan, a local resident who witnessed the attack.

Khan said the missiles flattened several residences and an adjoining girls' seminary. But he denied reports that a separate madrassa founded by Haqqani, an associate of Osama bin Laden, was also struck during the attack.

Haqqani and his son Sirajuddin were not in the compound when it was targeted but some of the Taliban commander's relatives, including his sister, were reportedly killed and injured.

A security official in the area verified the death toll and said it could rise further because several seminary students were still trapped under tons of debris.

Local residents were hesitantly retrieving the bodies and the injured from the rubble, fearing more US missile strikes. Around two dozen people were reported injured, many of them with serious wounds, and taken to hospital in Miranshah.

According to Khan, drones have been flying over the area for the past few days and local residents also fired at them using their AK-47 assault rifles.

An army spokesman confirmed that explosions occurred near Miranshah but refused to give further details.

US forces in Afghanistan and the US Central Intelligence Agency operate pilotless aircraft that have carried out several airstrikes in the tribal belt believed to be refuge for al-Qaeda and Taliban fighters.

The US aerial strikes have surged, and Monday's attack was the sixth in recent weeks. Six people including women and children were killed Thursday when a missile fired from a US drone hit a house in Mohammad Khel area of North Waziristan.

US troops also conducted their first reported ground attack into Pakistani territory on Wednesday killing 20 people in Angor Adda area of South Waziristan.

Islamabad protested "the gross violation of Pakistan's territory and immense loss of civilian life" and summoned US Ambassador Anne W Patterson to lodge a formal protest.