U.S. military personnel stationed at Shamsi Air Base in Pakistan have started to leave after the country's government told them to go following a NATO attack that killed 24 Pakistani soldiers near the Afghan border.
"Two U.S. cargo planes reached Shamsi Airport and the loading of the equipment and other cargo items has also started," an official privy to developments at Shamsi base told NBC News.
More than 70 U.S. Marines and CIA operatives who were present at Shamsi Base are due to leave.
Shamsi Air Base, situated in Baluchistan Province in south-west Pakistan, was used by the CIA to operate drone aircraft, which carried attacks inside Pakistan tribal areas.
Military ties between Pakistan and U.S. have hit an all-time low following the NATO attack, with Pakistan's military canceling all official visits to the U.S.
One U.S. government source told Reuters the United States has spent months preparing for a possible eviction from the Shamsi base by building up other drone launching and staging capability.
Earlier this year, after the U.S. raid that killed al-Qaida leader Osama bin Laden, some Pakistani officials demanded that Washington vacate the Shamsi facility.
At the time, however, U.S. officials said that American personnel would remain at the base and would continue to conduct drone flights in pursuit of militants.
But in one concession, the United States stopped conducting lethal drone operations from that base and limited operations to surveillance flights.
Vacating the air base was seen more as an inconvenience rather than a critical blow to drone operations, which the United States also conducts from Afghanistan and possibly elsewhere.
The unmanned aerial vehicles may have a longer flight from Afghanistan but they are capable of hovering overhead for hours as they seek to spot suspicious activity and follow militants.
U.S. officials are reluctant to openly talk about drone operations because they are considered a covert CIA activity.