Following a three-day fact-finding visit to Pakistan, the United Nations terrorism and human rights envoy issued a statement calling the U.S. drone strikes in Pakistan a violation of international law.
"The position of the government of Pakistan is quite clear: It does not consent to the use of drones by the United States on its territory and it considers this to be a violation of Pakistan's sovereignty and territorial integrity," said Ben Emmerson, U.N. special rapporteur on counterterrorism and human rights.
"As a matter of international law, the U.S. drone campaign in Pakistan is … being conducted without the consent of the elected representatives of the people or the legitimate government of the state," said Emmerson, who is British and has been investigating the impact of U.S. drone attacks in Pakistan's tribal areas on the civilian population.
He is expected to issue a final report to the United Nations in October.
The CIA-administered program targets al Qaeda and Taliban leaders in Pakistan's tribal areas near the border of Afghanistan. The areas are largely self-governed with a porous border and known to have extremists easily crossing between the two countries.
U.S. State Department spokeswoman Victoria Nuland would not comment directly on the legal implications of the strikes, citing classified intelligence, but told ABC News on Friday that the U.S. has seen Emmerson's statement and will await a final report before commenting further.
"We have a strong ongoing counterterrorism dialogue with Pakistan, and that will continue," she said.
Pakistan has been very vocal in its opposition to the program. The Ministry of Foreign Affairs has claimed there have been at least 330 drone strikes within Pakistan since 2004 that have killed at least 2,200 people and seriously injured 600 more. However, the government has not been able to report how many of those killed have been civilians, confirming at least 400 as non-combatants but estimating the number is likely much higher.
Pakistan's ambassador the United States, Sherry Rehman, told reporters last month that even within Pakistan's partisan and fractured politics there is one issue all Pakistani politicians agree on: Drone strikes cross a red line.
"We don't see drones as productive at all," she said, arguing that, in fact, the attacks have had the opposite effect of their intention - sparking anger that has fueled extremism in the tribal areas rather than rooting out terrorists.
While Rehman said that the United States and Pakistan will continue to cooperate on combating terrorism, she dismissed the idea that Pakistan is collaborating or turning a blind eye to the U.S. campaign.
"There is no policy of quiet complacency. No wink and nod," she said.
Former U.S. Ambassador to Pakistan Cameron Munter told the The Daily Beast last year that his concerns were not over the drone program's validity, but its implementation.
"The use of drones is a good way to fight the war. But you're going to kill drones if you're not using them judiciously," Munter said.
"The problem is the political fallout," he told the Daily Beast, citing examples where Pakistani civilians would come to him with bodies of little girls who they said were killed by drone strikes. "Do you want to win a few battles and lose the war?"
Munter is not the only current or former U.S. official to question the legality of the strikes. During CIA director John Brennan's confirmation hearing last month, several senators on the Foreign Relations Committee questioned whether the Obama administration was overstepping its bounds by launching drone strikes, including against American citizens, without any congressional or judicial oversight.
Brennan admitted that the administration could be more transparent about the number of civilians killed during a strike, but defended the program.
"We only take such actions as a last resort, to save lives when there is no other alternative," he told the committee.