Security officials in Pakistan say missiles fired from a U.S. drone have killed at least 18 suspected militants in the country's northwest, the fifth such attack in a week.

Officials say three compounds were hit Friday in the North Waziristan tribal agency, a known hub for Taliban and al-Qaida-linked militants. Several people were wounded in the strikes.

The attack was the fifth since August 18, with a total of 35 suspected militants killed in North Waziristan in the last week.

Friday's drone strike comes a day after Pakistan's foreign ministry summoned a senior U.S. diplomat to protest the attacks, calling them “unlawful, against international law and a violation of Pakistan's sovereignty.”

Foreign Ministry spokesman Moazzam Ahmad Khan repeated Pakistan's objection to drone strikes during a weekly press briefing Friday in Islamabad. Khan said Pakistan is working with the United States “to come up with a mutually acceptable solution.”

Pakistan has repeatedly criticized drone attacks, but U.S. officials say the strikes are an important tool in defeating the insurgents.

Elsewhere in Pakistan's northwest Friday, military officials say security forces repulsed an attack on a checkpoint in Dir by some 100 militants who crossed into the tribal agency from across the Afghan border. At least five militants were killed in the ensuing fighting, the remaining attackers fled.

In neighboring Bajaur tribal agency, local officials say militants from Afghanistan raided a remote village and kidnapped several members of a pro-government militia.

And in nearby Orakzai tribal agency, the military says eight militants were killed in clashes Friday.

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