Pakistani officials say U.S. drones have fired missiles at a compound in the country's northwest tribal region, killing eight suspected militants.

Thursday's drone attack took place in the Razmak area of North Waziristan along the Afghan border, a major hub for Taliban and al-Qaida-linked militants. Officials say at least two other militants were wounded.

It was the third such strike in as many days. On Wednesday, Pakistani officials said a drone attack in neighboring South Waziristan killed at least 16 militants. And another drone strike in North Waziristan on Tuesday killed seven militants.

Elsewhere in the country's northwest, authorities say Pakistani security forces killed at least 22 militants in the Orakzai tribal agency.

No independent confirmation of the incidents is available because journalists are barred from the region.

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.

Elsewhere in Pakistan, police say at least three suicide bombers detonated a car full of explosives in the southern port city of Karachi. Two police officers were killed in Wednesday's attack.