>>>LONDON - The United States' use of unmanned drones to strike terrorists is coming under increasing scrutiny. Those in favor say the drone strikes have been highly effective, but critics suggest they could violate international law. The New York Times claimed Sunday it had uncovered a secret deal between the U.S. and Pakistan over the use of drones in Pakistani airspace.

Unmanned drones are being used with increasing frequency in fighting terrorist groups like al-Qaida.

A recent analysis by the New America Foundation estimated drone strikes in Pakistan and Yemen since 2004 have killed up to 3,238 militants and as many as 368 civilians.

Professor Christopher Coker of the London School of Economics is author of Warrior Geeks: How 21st Century Technology Is Changing The Way We Fight And Think About War.

“There are six American bases - four in the United States, one in Germany and one in South Korea - and that’s where most of the drone strikes are launched from. And they have chaplains and psychologists now in the room monitoring; they have machines monitoring stress levels, also monitoring concentration levels," said Coker. "And there is, of course, a chain of command. So you [the pilots] spend about eight hours looking at the screen day after day and occasionally you get the command to actually fire.”

The New York Times newspaper alleged Sunday that Pakistan is allowing U.S. drones in its airspace in return for targeted killings of Pakistan’s enemies by the drones. The Pakistani government strongly denied the allegations; the U.S. government did not comment.

The drone strikes have prompted street protests in Pakistan. Arif Niazi is a lawyer in Islamabad.

"These ongoing attacks are blatant aggression, an intrusion into my country and a violation of its sovereignty," said Niazi.

Marco Roscini, an expert on international law at the University of Westminster, says the legality of current drone strikes is murky.

“There is a huge need for clarification and there’s a huge need for transparency," said Roscini. "You know that most of the strikes are now allegedly carried out by the CIA and their covert operations. So we don’t know why, who or when an individual is put on the targeted list.”

The decision on whom to target is a key distinction between CIA drone strikes and the military, says Professor Christopher Coker of the London School of Economics.

“The military can only actually take out someone if they know 100 percent that it’s a bad guy," he said. "The CIA will take you out on the basis that your behavior leads them to suspect that you may be a bad guy.”

Supporters of drone strikes point to the killing of numerous high-profile targets - such as last year's strike in Pakistan that killed the then number two in al-Qaida, Abu Yahya al-Libi.

At his nomination hearing before the Senate Intelligence Committee in February, CIA Director John Brennan was questioned about the use of drones to kill U.S. citizens suspected of joining terror groups.

“I think any Americans who did that, should know well, that they are in fact part of an enemy against us, and the United States will do everything possible to destroy that enemy to save American lives," said Brennan.

With most NATO ground forces withdrawing from Afghanistan at the end of 2014, analysts says drones could play a bigger role in the West’s fight against al-Qaida and other terrorist groups.