A British human rights lawyer is to lead a U.N. inquiry into the legality of American drone attacks and their impact on civilians in Pakistan, Afghanistan and several other countries.

Ben Emmerson, QC, who will head a team of international experts in his capacity as a U.N. Special Rapporteur on Human Rights and Counter-terrorism, said here on Thursday that the “exponential’’ rise in the use of drone technology represented “a real challenge to the framework of international law”.

“Those states using this technology and those on whose territory it is used are under an international law obligation to establish effective independent and impartial investigations into any drone attack in which it is plausibly alleged that civilian casualties were sustained.’’

The inquiry, which will examine 25 attacks in Pakistan, Afghanistan, Yemen, the Palestinian territories and Somalia, follows anger over the loss of innocent civilian lives. Critics have called them “extra-judicial’’ killings.

According to the London-based Bureau of Investigative Journalism, American drone attacks in Pakistan since 2004 had killed up to 3,461 people, including nearly 900 civilians.

“One area the inquiry is expected to examine is the deliberate targeting of rescuers and funeral-goers by the CIA in Pakistan, as revealed in an investigation by the Bureau for the Sunday Times,’’ the Bureau said.

Mr. Emmerson said the U.N. had decided to investigate the complaints as a “final resort’’ because America and its allies who should have done so had not done it.

“This is not, of course, a substitute for effective official independent investigations by the states concerned,’’ he emphasised.

In response to a question from reporters, he denied that the inquiry was unfairly singling out America. Pointing out that 51 countries had the technology to launch drone attacks, he said Britain was already cooperating and Washington had “not ruled out full cooperation’’.