Intelligence officials in northwest Pakistan say a U.S. drone strike in the country's restive tribal region near the Afghan border has killed at least six militants.

Authorities say the missile strike Monday occurred near Wana, the main town of the South Waziristan region, the country's main stronghold of Taliban and al-Qaida linked militants.

U.S. drone strikes against insurgents in northwest Pakistan have been a source of friction between the two countries.

U.S. officials have never publicly acknowledged the use of drones inside Pakistan, but privately they have confirmed the strikes to various news outlets, saying the operations have killed mostly militants.

The attack comes after the reported death of al-Qaida operative Ilyas Kashmiri in a U.S. drone strike in the tribal region Friday.

On Sunday, Pakistan officials said at least 24 people were killed and more than 45 were wounded in two separate explosions in the northwestern cities of Matani and Nowshera.

.