Human rights group Amnesty International has called on the US to investigate reports of civilians hit by CIA drone strikes aimed at militants in Pakistan.
It is concerned that the attacks may have resulted in unlawful killings that constitute illegal executions or war crimes, even though the US insists the strikes are legal.
"We cannot find any justification for these killings. There are genuine threats to the USA and its allies in the region, and drone strikes may be lawful in some circumstances," said Mustafa Qadri, Amnesty International's Pakistan researcher. "But it is hard to believe that a group of labourers, or an elderly woman surrounded by her grandchildren, were endangering anyone at all, let alone posing an imminent threat to the United States."
Amnesty called on the US to comply with its obligations under international law by investigating the killings documented in the report and providing victims with "full reparation."
The US carried out its first drone strike in Pakistan in 2004 and has launched nearly 350 more since, most in North Waziristan, a major militant sanctuary near the Afghan border. President Barack Obama significantly increased attacks when he took office in 2009, and the number peaked the following year with over 100 strikes. The frequency has steadily dropped since, partly because of growing tension between Pakistan and the US There have only been around two dozen strikes so far this year.
Pakistani officials regularly denounce the attacks in public as a violation of the country's sovereignty, but senior members of the government and the military are known to have supported them in the past.
"Amnesty International is also extremely concerned about the failure of the Pakistani authorities to protect and enforce the rights of victims of drone strikes," said the report. "Pakistan has a duty to independently and impartially investigate all drone strikes in the country and ensure access to justice and reparation for victims of violations."
Amnesty said victims they interviewed with no apparent connection to militant groups have either received no compensation or inadequate assistance from the Pakistani government.
Relatives of 68-year-old grandmother Mamana Bibi told Amnesty she was killed by a missile in October last year as she was collecting vegetables in a family field in the North Waziristan tribal area,. Three of her grandchildren were wounded in the strike.
The US considers its drone programme to be a key weapon against insurgent groups that it says stages cross-border forays into neighbouring Afghanistan. But the belief, widespread in Pakistan, that the strikes kill large numbers of civilians sparks resentment and complicates the two countries' ability to coordinate efforts against militants based in the country, including al-Qaida.
An even deadlier incident noted by the report - titled "'Will I be next?' US drone strikes in Pakistan"- occurred in North Waziristan in July last year. Witnesses said a volley of missiles hit a tent where a group of men had gathered for an evening meal after work, and then a second struck those who came to help the wounded, one of a number of attacks that have hit rescuers, the rights group said.
Witnesses and relatives said that total of 18 male labourers with no links to militant groups died, according to Amnesty. Pakistani intelligence officials at the time identified the dead as suspected militants.