"Any object entering into our airspace, including US drones, will be treated as hostile and be shot down," a senior unnamed Pakistani military official was quoted as saying by NBC News.
The defence policy was changed after a NATO air strike on two military border posts killed 24 Pakistani soldiers on November 26. Following the air strike, army chief Gen Ashfaq Parvez Kayani issued a communique that gave troops in the field full liberty to respond to any future attacks without consulting their superiors.
Kayani issued multiple directives since the November 26 attack, including orders to shoot down US drones, senior military officials said.
Pakistan also shut down all NATO supply routes and asked the US to vacate the Shamsi airfield in Balochistan province by December 11. The airbase is reportedly used by the Central Investigation Agency-operated drones that target militants in the tribal areas along the Afghan border.
A senior military official in Quetta, the capital of Balochistan, told NBC News on Sunday that the evacuation of the airbase would be completed within the deadline. Pakistan's paramilitary Frontier Corps took control of the airbase on Saturday evening after most US military personnel left. Civil aviation officials too moved in.
US President Barack Obama stepped up the drone campaign after he took office. US officials say the drone strikes produced major successes in decimating the central leadership of the Al Qaeda.
Since 2004, US drones have carried out more than 300 attacks inside Pakistan.