A senior United Nations official said Wednesday that the U.S. should halt the CIA’s drone campaign against al-Qaida and Taliban forces in Pakistan, charging that the official secrecy surrounding the strikes violates the legal principle of international accountability.

But a report by Philip Alston, the United Nations special rapporteur on extrajudicial, summary or arbitrary executions, stopped short of declaring the CIA program illegal.

Alston presented a 29-page report to the U.N.’s Human Rights Council in Geneva on Wednesday that focused on so-called targeted killings by countries such as Russia and Israel as well as the United States.

“It is an essential requirement of international law that States using targeted killings demonstrate that they are complying with the various rules governing their use in situations of armed conflict,” Alston said in a press release. “The greatest challenge to this principal (sic) today comes from the program operated by the U.S. Central Intelligence Agency. The international community does not know when and where the CIA is authorized to kill, the criteria for individuals who may be killed, how it ensures killings are legal, and what follow-up there is when civilians are illegally killed.”

Alston noted that some commentators have argued that CIA personnel involved in drone killings are committing war crimes because, unlike the military, they are “unlawful combatants.” But he said, “this argument is not supported” by international humanitarian law.

“This agency’s operations unfold within a framework of law and close government oversight,” said George Little, a CIA spokesman.