PESHAWAR – Unmanned U.S. aircraft fired four missiles at a house in northwest Pakistan before dawn Wednesday, killing 16 suspected militants, Pakistani intelligence officials said.

The drone strike elicited a swift condemnation by the Pakistani government, which released a statement saying the strikes are a violation of its sovereignty.

The attack in the Sarai Darpa Khel area of the North Waziristan tribal region also wounded two suspected militants, said the officials, speaking on condition of anonymity because they were not authorized to talk to the media.

The suspected militants who were targeted were believed to be from the Afghan Haqqani network. U.S. officials consider the Haqqani network to be one of the most dangerous militant factions fighting American troops in neighbouring Afghanistan. The leadership of the Haqqani network pledges allegiance to Taliban chief Mullah Omar but operates fairly independently.

U.S. drone strikes have become a serious source of tension between Washington and Islamabad. The Pakistani government regularly denounces the strikes as a violation of the country’s sovereignty, even though senior officials are known to have supported some of the attacks in the past.

“The Government of Pakistan has consistently maintained that drone strikes are counter-productive, entail loss of innocent civilian lives and have human rights and humanitarian implications,” the Ministry of Foreign Affairs said in a statement Wednesday.

“These drone strikes have a negative impact on the mutual desire of both countries to forge a cordial and co-operative relationship and to ensure peace and stability in the region,” the ministry said.