Security officials in Pakistan say a U.S. drone strike has killed at least 16 people in the restive northwest tribal region near the Afghan border.

Authorities say drone-fired missiles hit three compounds Friday in North Waziristan, a known hub for Taliban and al-Qaida-linked militants.

The strikes come a day after Pakistan summoned a U.S. diplomat to protest drone strikes, calling them “unlawful.”

Pakistan has repeatedly criticized the drone strikes, saying they violate the country's sovereignty, but U.S. officials say the strikes are an important tool in defeating the insurgents.