The United States on Tuesday denied its drone strikes in Yemen and Pakistan and elsewhere infringed international law and said it did all it could to avoid civilian casualities.

The comments followed the publication of reports on the US drone war by two human rights groups, and came a day before Pakistani Prime Minister Nawaz Sharif is expected to bring up concerns about the US tactic at White House talks.

"We are reviewing these reports carefully," White House spokesman Jay Carney said.

"To the extent these reports claim that the US has acted contrary to international law, we would strongly disagree.

"The administration has repeatedly emphasized the extraordinary care that we take to make sure counterterrorism actions are in accordance with all applicable law."

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."

Earlier Amnesty International and Human Rights Watch unveiled reports detailing civilian casualties in a number of US operations in Pakistan and Yemen.

Human Rights Watch and Amnesty International are jointly calling on the US Congress to fully investigate the cases the two organizations have documented as well as other potentially unlawful strikes, and to disclose any evidence of human rights violations to the public. Those responsible for unlawful killings should be appropriately disciplined or prosecuted.

The groups called on Obama to provide a full legal rationale for targeted killings in Yemen and elsewhere.