Pakistani officials say U.S. drones have fired missiles at a vehicle in Pakistan's northwest tribal region, killing four suspected militants.

Authorities say the attack happened Monday in Degan village in North Waziristan on the Afghanistan border.

U.S. officials have never publicly acknowledged drone strikes against militants in Pakistan's tribal areas, but have anonymously confirmed such attacks to various news outlets.

Pakistan has condemned the strikes as a violation of the country's sovereignty, but they are believed to be carried out with the help of Pakistani intelligence.