The US has defended its drone strikes in Yemen and Pakistan, saying it takes "extraordinary care" to ensure they comply with international law.
The unmanned raids targeting terror suspects were a "course of action least likely to result in the loss of innocent life", the White House said on Tuesday.
The statement follows allegations by Human Rights Watch and Amnesty International of the unlawful killing of civilians by the Central Intelligence Agency-controlled drone strikes (also see: US drone attacks tantamount to war crimes, says Amnesty).
Pakistan's Prime Minister Nawaz Sharif on Tuesday urged the US to end drone attacks in his country. Speaking at the start of a visit to the US, Nawaz Sharif said the attacks violated his country's sovereignty, and were a "major irritant" in relations with Washington.
Drone warfare has become common in the US pursuit of al-Qaeda and the Taliban. Few details are known about these covert operations, which are directed by the CIA remotely from control rooms, often on other continents.
The new Amnesty International report has sought to document more evidence of civilian deaths in drone strikes than before, but some of the cases they have brought forth as examples were already known to the media.
White House spokesman Jay Carney said Washington was "reviewing the reports carefully".
"To the extent these reports claim that the US has acted contrary to international law, we would strongly disagree.
"The administration has repeatedly emphasised the extraordinary care that we take to make sure counter-terrorism actions are in accordance with all applicable law," he said.
Carney also said that by deciding to use drone aircraft against terror suspects, rather than sending in troops or using other weapons, Washington was "choosing the course of action least likely to result in the loss of innocent life." (Also see: Top US law schools had blasted drone strikes before Amnesty)