ISLAMABAD — Suspected U.S. drones fired missiles at vehicles today and hit a militant hide-out in a tribal region of northwestern Pakistan, killing at least nine insurgents, two officials said.

In the first attack, the drones fired four missiles at a vehicle and flattened a nearby house near Miran Shah, the main town in the North Waziristan tribal region, killing six militants, an army and an intelligence official said.

About 50 minutes later, drones fired three more missiles at a vehicle in Madakhel town, about 25 miles west of Miran Shah, killing three insurgents, the officials said on condition of anonymity because they were not authorized to talk to the media.

Other militants were also wounded in the two strikes, they said.

The U.S. has stepped up attacks in Pakistan’s tribal regions since December, when a suicide bomber killed seven CIA employees in neighboring Afghanistan. The latest attack came a day after a U.S. missile strike destroyed a militant facility in the same region, killing nine suspects.

Officials say some of the men slain in Tuesday’s attack in Datta Khel were believed to be foreigners who were in the stronghold of Hafiz Gul Bahadur, a warlord whose fighters are battling U.S. and NATO forces in Afghanistan.

Although Pakistan publicly opposes the attacks, saying they violate its sovereignty and fuel anti-Americanism among the population, it is believed to share intelligence with the Americans about the insurgents and their hide-outs.

Washington also refuses to publicly discuss the program, which uses unmanned drones, but officials say privately the attacks have killed several senior al-Qaida and Taliban commanders in recent years.

In Pakistan’s southwest city of Quetta, an explosion destroyed a house, police official Mohammad Nawaz said. Police recovered a man’s body as well as some literature about the banned Sunni extremist outfit, Lashkar-e-Jhangvi. Nawaz said authorities were trying to figure out if the victim was involved in bomb-making.