Updated

MIR ALI, Pakistan (AP) — A suspected U.S. drone fired missiles at a house in northwestern Pakistan on Monday, killing four people in the 20th such attack this month — nearly double the previous monthly record, intelligence officials said.

Almost all of the attacks this month have occurred in North Waziristan, part of Pakistan's semiautonomous tribal region that is largely out of the state's control and is dominated by militants who regularly stage attacks against U.S. troops in Afghanistan.

The house targeted Monday was located in Khushali, a village near Mir Ali, one of the major towns in North Waziristan, said the intelligence officials, speaking on condition of anonymity because they were not authorized to talk to the media.

The identities of the four people killed in the attack were not known, but the area is dominated by fighters led by the powerful militant commander Hafiz Gul Bahadur, said the officials.

Until now, the highest number of airstrikes inside Pakistan in a single month had been the 11 launched in January 2010 after a suicide bomber killed a Jordanian intelligence officer and seven CIA employees at a base in Afghanistan.

The U.S. refuses to publicly acknowledge the drone strikes, but officials have said privately that they have killed several senior al-Qaida and Taliban commanders.

Pakistani officials have criticized the strikes in the past as violations of the country's sovereignty, but such criticism has been muted in recent months despite the high number of attacks.

Many analysts believe Pakistan actually assists the U.S. in carrying out the strikes, especially when they target groups like the Pakistani Taliban that are at war with the state.