Pakistani security officials say a U.S. drone strike in a restive Pakistani tribal region near the Afghan border has killed seven militants.

Authorities say the U.S. fired four missiles on two militant vehicles Sunday in the Shawal district of North Waziristan, a region considered a stronghold of Taliban and al-Qaida insurgents.

Four militants were killed Saturday in a drone strike in the same region.

Drone strikes are a contentious issue between Washington and Islamabad.  Pakistan says the strikes violate its sovereignty, but the United States believes they are an important tool in the effort to defeat al-Qaida.