WASHINGTON — A senior United Nations official is expected to call on the United States next week to stop Central Intelligence Agency drone strikes against people suspected of belonging to Al Qaeda, complicating the Obama administration’s growing reliance on that tactic in Pakistan.

Philip Alston, the United Nations special rapporteur on extrajudicial, summary or arbitrary executions, said Thursday that he would deliver a report on June 3 to the United Nations Human Rights Council in Geneva declaring that the “life and death power” of drones should be entrusted to regular armed forces, not intelligence agencies. He contrasted how the military and the C.I.A. responded to allegations that strikes had killed civilians by mistake.

“With the Defense Department you’ve got maybe not perfect but quite abundant accountability as demonstrated by what happens when a bombing goes wrong in Afghanistan,” he said in an interview. “The whole process that follows is very open. Whereas if the C.I.A. is doing it, by definition they are not going to answer questions, not provide any information, and not do any follow-up that we know about.”

Mr. Alston’s views are not legally binding, and his report will not assert that the operation of combat drones by nonmilitary personnel is a war crime, he said. But the mounting international concern over drones comes as the Obama administration legal team has been quietly struggling over how to justify such counterterrorism efforts while obeying the laws of war.