UNITED NATIONS — US drone strikes against suspected terrorists in Afghanistan and Pakistan could be breaking international laws against summary executions, the UN's top investigator of such crimes said.

"The problem with the United States is that it is making an increased use of drones/Predators (which are) particularly prominently used now in relation to Pakistan and Afghanistan," UN Special Rapporteur on Extrajudicial Executions Philip Alston told a press conference.

"My concern is that drones/Predators are being operated in a framework which may well violate international humanitarian law and international human rights law," he said.

US strikes with remote-controlled aircraft against Al-Qaeda and Taliban targets in Afghanistan and northwestern Pakistan have often resulted in civilian deaths and drawn bitter criticism from local populations.

"The onus is really on the United States government to reveal more about the ways in which it makes sure that arbitrary extrajudicial executions aren't in fact being carried out through the use of these weapons," he added.

Alston said he presented a report on the matter to the UN General Assembly.

He urged the United States to be more forthright about how and when it uses drone aircraft, something about which the US Defense Department and Central Intelligence Agency (CIA) usually keep silent.

"We need the United States to be more up front and say, 'OK, we're willing to discuss some aspects of this program,' otherwise you have the really problematic bottom line that the CIA is running a program that is killing significant numbers of people and there is absolutely no accountability in terms of the relevant international laws," Alston said.

Since August 2008, around 70 strikes by unmanned aircraft have killed close to 600 people in northwestern Pakistan.

"I would like to know the legal basis upon which the United States is operating, in other words... who is running the program, what accountability mechanisms are in place in relation to that," Alston said.

"Secondly, what precautions the United States is taking to ensure that these weapons are used strictly for purposes consistent with international humanitarian law.

"Third, what sort of review mechanism is there to evaluate when these weapons have been used? Those are the issues I'd like to see addressed," the UN official said.