Amnesty International has delivered a scathing assessment of America’s drone program, saying some attacks could amount to war crimes.
The human rights group has investigated a series of strikes which it says have killed innocent people.
The Pakistani government claims that missiles fired from unmanned aerial vehicles are now responsible for between 400 and 900 civilian deaths.
The US says the strikes have saved lives and their actions are legal, but the Amnesty investigation says drones have killed civilians against international law.
“But what’s clear is that this gives the US, in effect, a licence to kill beyond the reach of the courts and international standards,” said Amnesty spokeswoman Polly Truscott.
Amnesty visited Pakistan’s north Waziristan tribal region, home to Taliban and Al Qaeda militants.
Among the nine drone attacks it investigated is the case of 68-year-old Mamana Bibi who was killed by a missile last year as she picked vegetables.
“It seems impossible to imagine that anyone could have considered Mamana Bibi to have been an insurgent,” Ms Truscott said.
“It’s very much a case of unlawful killing.”
Australia accused of collusion
The report says Pakistani authorities are partly responsible allowing the attacks to happen.
Australia is mentioned too, accused of collusion by providing intelligence reportedly through the Pine Gap spy base near Alice Springs.
“Australia, the UK, Germany and others all must ensure that they do not provide such assistance where it may be used to permit international law violations,” Ms Truscott said.
This month the UN voiced its concern, urging the US to be more transparent about civilian deaths.
President Barack Obama has been sensitive to the criticism and in a speech earlier this year defended the attacks, while acknowledging the civilian toll.
“But as commander in chief I must weigh these heart-breaking tragedies against the alternatives,” he said.
The use of force, Mr Obama maintains, is necessary.
“So this is a just war, a war waged proportionally in last resort and in self-defence,” he said.
But observers like Steve Gross from the Conservative Heritage Foundation say drones have been effective in dismantling America’s enemies.
He also questions the hundreds of civilian deaths quoted by human rights groups.
“I’m confident intelligence services do what they can to reduce civilian deaths while prosecuting the war on terror, as they must,” he said.
“We’re in the middle of an asymmetric war with non-state terrorist organisations who have no interest in reporting factually about what happens on the battlefield, and it’s in their interests for propaganda purposes to exaggerate civilian deaths.”
Drones likely to be raised as Pakistan PM visits US
Pakistan’s PM, Nawar Sharif, is in Washington this week and will meet Mr Obama at the White House.
The issue of drones is likely to be raised, one of a number of delicate matters testing the bilateral relationship.
Akbar Ahmed, who served as Pakistan’s high commissioner to Britain and now lives in Washington, says the US has been using the wrong tactics against the wrong enemy and getting the wrong results.
“I think it should have understood the tribal nature of these societies, the fact that they already were in turmoil … and that these were impoverished areas desperate for development.
“Now there are some bad guys among them, militants among them … but the way to go about it is not to antagonise entire societies.
“What the drone does it literally antagonises the entire section or clan or tribe, which means for every one bad guy killed, you end up antagonising maybe 10,000, 15,000, and therefore the lines for the suicide bombers are unending.”
Mr Ahmed says the more proportionate response is the big question facing Mr Sharif as he visits Washington.
“I don’t think he wants to make it very visible, but I am sure that that will come up with president Obama because it is high upon his list of priorities,” he said.
“There have been politicians like Imran Khan who said ‘if ever I became PM, my first act will be to ask the Pakistan air force to shoot down the drones’, and just that act would have enormous implications for international relations.
“So feelings in Pakistan are very, very high around this subject of the drones. As I said, it’s become very symbolic now, something poisonous in the relationship between the US and Pakistan.”