UNITED NATIONS – A U.N. human rights investigator warned the United States Tuesday that its use of unmanned warplanes to carry out targeted executions may violate international law.

Philip Alston said that unless the Obama administration explains the legal basis for targeting particular individuals and the measures it is taking to comply with international humanitarian law which prohibits arbitrary executions, "it will increasingly be perceived as carrying out indiscriminate killings in violation of international law."

Alston, the U.N. Human Rights Council's investigator on extrajudicial, summary and arbitrary executions, raised the issue of U.S. Predator drones in a report to the General Assembly's human rights committee and at a news conference afterwards, saying he has become increasingly concerned at the dramatic increase in their use, especially in Afghanistan and Pakistan, since June.

He said the U.S. response — that the Geneva-based council and the General Assembly have no role in relation to killings during an armed conflict — "is simply untenable."

"That would remove the great majority of issues that come before these bodies right now," Alston said. "The onus is really on the government of the United States to reveal more about the ways in which it makes sure that arbitrary executions, extrajudicial executions are not, in fact, being carried out through the use of these weapons."

Alston's warning comes as President Barack Obama is weighing how to overhaul the U.S. approach to the Afghan conflict.

Gen. Stanley McChrystal, the U.S. commander in Afghanistan, wants as many as 40,000 more troops while Vice President Joe Biden favors maintaining the current troop strength of around 68,000 and significantly increasing the use of unmanned drones and special forces for the kind of surgical anti-terror strikes that have been successful in Pakistan, Somalia and elsewhere.

Alston, a law professor at New York University, said that while there may be circumstances where the use of drones "to carry out targeted executions" is consistent with international law, this can only be determined in light of information on the legal basis for selecting certain individuals.

"What we need then is the U.S. to be more up front and say 'OK, we're prepared to discuss some aspects of this program,'" he said.

Alston said the U.S. should provide details on use of drones, disclose what precautions it takes to ensure the unmanned aircraft are used strictly for purposes consistent with international humanitarian law, and what measures exist to evaluate what happened when their weapons have been used.

"Otherwise, you have the really problematic bottom line -- which is that the Central Intelligence Agency is running a program which is killing significant numbers of people, and there is absolutely no accountability in terms of the relevant international laws," he said.

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