The US government only acknowledges its role in targeted killings in general terms, refusing to take responsibility for individual strikes or provide casualty figures, including civilian deaths, Human Rights Watch said in their report on drone attacks in Yemen
The Yemeni authorities have been almost as silent, the rights organisation said. Both governments have declined to comment on the six strikes that Human Rights Watch investigated.
An interactive map published by Amnesty International details recent drone attacks the human rights organisation says the US carried out in northwest Pakistan.
Amnesty International found evidence that a number of civilians, including an elderly woman and a group of young labourers, were killed in drone strikes in North Waziristan between January 2012 and August this year.
Researchers from Human Rights Watch have called on the US to assess the impact of drone attacks in Yemen, which they say are in "clear violation of the laws of war."
The calls come as Human Rights Watch and Amnesty International released two reports investigating who died as a result of the attacks in Yemen and Pakistan.
The US says it is taking all possible precautions during targeted killings, but it has unlawfully killed civilians and struck questionable military targets in Yemen.
Yemenis told us that these strikes make them fear the US as much as they fear al-Qaeda.
The US should investigate attacks that kill civilians and hold those responsible for violations to account. It's long past time for the US to assess the legality of its targeted killings, as well as the broader impact of these strikes on civilians.
Human Rights Watch are calling for the US government to assess the legality of drone strikes in Yemen, after their study of six such attacks found that the majority of those killed were civilians.
The strikes investigated by the rights group, between 2012 and 2013, found at least 57 of the 82 people killed were civilians; equivalent to 70% of the casualties.
Amnesty International has accused the US government of unlawfully killing civilians in its drone campaign in the tribal regions of north-west Pakistan.
The rights group also said the US was launching so-called "rescue attacks" in which those who attempted to help victims of the first unlawful killing were injured in a second lethal strike.
In a film produced to coincide with their major study of the impact of drone attacks on local populations in Northern Waziristan, the family of a woman who is said to have died in an attack describe their grief and trauma from the method of her death.
Obama has pledged to reduce the number of drone strikes used, and in May this year switched responsibility for launching a drone attack from the CIA to the Department of Defence.
Amnesty International has called on the US government to "come clean" about the number of unmanned aircraft or drone attacks they are carrying out in north-west Pakistan.
In a scathing report that accuses the US of unlawful killing of civilians that could amount to war crimes, Amnesty said many civilians are being caught in the cross fire of an increasingly dangerous armed conflict waged between US drones, armed al-Qaeda linked groups and the Pakistani army.
The secrecy surrounding the nature as well as the number of attacks taking place means that victims are left without the possibly of compensation, and Pakistani authorities have been accused of neglecting the human rights of residents across the tribal regions, leading to ever-greater instability.
The US has been accused of carrying out unlawful attacks on civilians that could amount to war crimes in Pakistan and Yemen, two scathing reports into the use of drones revealed today.
Amnesty International reviewed 45 known drone strikes that took place in North Waziristan in northwest Pakistan between January 2012 and August 2013 found evidence that a number of civilians, including an elderly woman, and a group of young labourers, were killed in attacks.
Human Rights Watch said their evaluations of six US drone strikes in Yemen found that two of the attacks killed civilians indiscriminately "in clear violations of the laws of war" and the others may have targeted people who were not legitimate targets, or caused disproportionate civilian deaths.
Both reports are based on interviews with dozens people living in areas targeted by US drones.
Amnesty International and Human Rights Watch are jointly calling on the US Congress to investigate the cases documented by their researchers, and disclosed any evidence of human rights violations or war crimes, and prosecute those responsible.
The percentage of missions in which British drones in Afghanistan have used weapons doubled between 2008 and 2012, data released by the Ministry of Defence showed.
In 2008, there were 296 missions over Afghanistan and one or more missiles was deployed by a British-operated Reaper drone on 14 missions, 5 per cent of the total number of sorties.
But in 2012, there were 892 missions by British drones, with weapons being fired on 92 occasions - more than 10 per cent of all sorties.
An RAF spokesman said the drones have "played a vital role supporting military operations in Afghanistan and saving countless UK and allied forces' lives."
He added that the "number of Reaper sorties and associated weapons releases has risen as the number of UK Reaper assets and sorties has increased."
US Secretary of State John Kerry has arrived in Islamabad for talks with the Pakistan government to try to ease tensions over drone strikes near the Afghanistan border, the Associated Press is reporting.
US President Obama has outlined plans to limit the use of US drones, saying they must be targeted against terrorists when a threat was "imminent." Responsibility for launching a drone has been transferred from the CIA to the US Department of Defence. He said:
"To say a military tactic is legal, or even effective, is not to say it is wise or moral in every instance.
"Any drone strike will only be launched when a terrorism suspect cannot be captured. The United States will respect state sovereignty and will limit strikes to al Qaeda or associated targets.
"And before any strike is taken, there must be near-certainty that no civilians will be killed or injured - the highest standard we can set."