Pakistani officials say a U.S. drone strike has killed at least 3 people in the country's northwest, near the Afghan border.

Sources say at least two missiles hit near Miran Shah, the main town in the North Waziristan tribal agency, a known stronghold of al-Qaida and Taliban-linked militants.

Unofficial reports say a woman was among those killed in Wednesday's attack.

It was one of three such deadly strikes in the region this month. At least 21 militants were killed in the other two attacks.

Pakistan has repeatedly criticized U.S. drone attacks as a violation of the country's sovereignty, but American officials say the strikes are a key tool in defeating militants.