14 March 2011
Most of the victims were believed to be civilians attending a tribal meeting near the regional capital, Miranshah.
Earlier reports had said militants were among the dead. The area is an al-Qaeda and Taliban stronghold and US drones regularly target the region.
The latest deaths come amid rising anti-US anger in Pakistan after a CIA contractor was acquitted of murder.
The freeing of Raymond Davis has sparked protests across Pakistan.
Many people are angered that so-called "blood money" reported to amount to more than $2m (£1.24m) was paid to the families of the two men he killed in Lahore. The relatives then pardoned him under Sharia law and the court freed him.
Militants not 'present'
The BBC's M Ilyas Khan in Islamabad says Thursday's drone strike is thought to have killed more civilians than any other such attack since 2006.
Officials say two drones were involved in the latest attack, in the Datta Khel area 40km (25 miles) west of Miranshah.
One missile was fired at a car carrying suspected militants. Local tribesmen say the drones then fired another three missiles at their meeting, or jirga.
Our correspondent says the vehicle was moving close to the site where the jirga was being held in the open. The missiles hit the vehicle as well as the jirga.
According to the tribesmen, they meeting was being held to discuss a local land dispute over the ownership of chromite deposits in the area. They say that no militants were present at the time.
Officials said the drones were targeting militants linked to Taliban commander Hafiz Gul Bahadur. One of his commanders, identified as Sharabat Khan, was in the vehicle hit in the attack and was killed, one local official told the BBC.
But most of the dead were tribal people - elders, local traders and members of the tribal police.
The official said 15 bodies had been found intact and identified by local people before being buried. Some of the dead were carried across the border into Afghanistan from where they had come.
Other bodies were blown to pieces, making a body count difficult to determine. There is no way of independently confirming casualty details as the media is denied access to the area.
It is the second drone strike in the area in as many days. On Wednesday a missile strike killed five suspected militants in Datta Khel.
US drone attacks have escalated in the region since President Barack Obama took office. More than 100 raids were reported in the area last year.
The US does not routinely confirm that it has launched drone operations, but analysts say only American forces have the capacity to deploy such aircraft in the region.
The Pakistani authorities deny secretly supporting drone attacks, which
have caused great anger in the country. A number of militants, some of them
senior, have been killed in the raids, but many civilians have also died.