A volley of U.S. missiles killed 15 alleged militants in an extremist stronghold in northwestern Pakistan on Friday, the second such strike in less than 12 hours, officials said.

A volley of U.S. missiles killed 15 alleged militants in an extremist stronghold in northwestern Pakistan on Friday, the second such strike in less than 12 hours, officials said.

The Obama administration regards missile attacks from drone aircraft as a key weapon against al-Qaida and the Taliban close to the Afghan border. Last month, al-Qaida’s reputed No. 3 official, Mustafa al-Yazid, was killed in a similar strike in the North Waziristan region.

Six missiles were fired in Friday’s attack on a house in a village close to the border, two intelligence officers said. They were not authorized to give their names.

Yousaf Khan, a government administrator in the region’s main town of Miran Shah, said 15 alleged militants were killed.

He said officers were still gathering information about the identities of the victims.

Late Thursday, two people were killed in another strike in North Waziristan. Officials did not say whether they were believed to be militants.

Pakistan is under pressure to launch a military offensive in the region, but the army says it is too stretched and committed to other parts of the border region to do so anytime soon.

There have been more than 35 suspected missile strikes this year alone, the highest tempo since the attacks began in earnest in 2008.

The attacks have killed many hundreds of people, most identified by Pakistani officials after the strikes as suspected militants. There have also been many accounts of civilian deaths. Washington does not acknowledge firing the missiles, let alone say who they are killing.

Critics say the attacks may violate international law and amount to extrajudicial killings.

Pakistan’s government publicly opposes the strikes to prevent domestic critics from accusing it of conspiring with United States in killing its own citizens. But it is widely believed to provide intelligence assistance for at least some of the strikes.

The drones either take off from bases across the border in Afghanistan or reportedly from secret bases within Pakistan.