Pakistan - A suspected U.S. drone fired missiles at a house and a vehicle in northwestern Pakistan on Monday, Pakistani intelligence officials said, killing four alleged militants in an attack that could signal the program is picking up steam after strained relations halted strikes late last year.

The U.S. held off on carrying out drone attacks in Pakistan for nearly two months after American airstrikes accidentally killed 24 Pakistani soldiers at two posts along the Afghan border on Nov. 26. The deaths outraged Pakistan, which retaliated by closing its border crossings to supplies meant for NATO troops in Afghanistan and kicking the U.S. out of a base used by American drones.

U.S. drone attacks have been a source of tension between the two countries. Although Pakistan is widely believed to have supported the strikes in the past, that cooperation has become strained as the relationship between the two countries has deteriorated.

The U.S. halted strikes until Jan. 10, when missiles hit a house in the North Waziristan tribal area in an attack that American officials said killed a key al-Qaida operations planner, Aslam Awan. The U.S. carried out another attack two days later.

Monday's strike in North Waziristan's Deegan village was the third since the attacks resumed. Initial reports indicated the alleged militants killed were foreigners, said Pakistani intelligence officials, speaking on condition of anonymity because they were not authorized to talk to the media.