PESHAWAR, Pakistan » Unmanned U.S. aircraft fired four missiles at a house in northwest Pakistan before dawn Wednesday (Tuesday in Hawaii), 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 neighboring 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 cooperative relationship and to ensure peace and stability in the region," the ministry said.

U.S. officials rarely provide details publicly about the covert CIA drone program in Pakistan.

The U.S. has urged Pakistan to take military action against the Haqqani network in North Waziristan, but Islamabad has so far refused. The Pakistani army says its forces are stretched too thin fighting domestic Taliban militants in other parts of the tribal region.

But many analysts believe the military is reluctant to anger the Haqqani network because of its historical ties with the group and the belief that it will play an important role in Afghanistan after foreign forces withdraw from the neighboring country.

Elsewhere in northwest Pakistan, militants attacked a police post before dawn Wednesday and killed six policemen, said a local government administrator, Habibullah Khan.

Ten policemen were wounded in the attack about 25 kilometers (15 miles) southeast of the city of Peshawar, said another government official, Feroz Shah. The post was staffed by both paramilitary police from the Frontier Constabulary force and also by tribal policemen.

Khan said policemen retaliated in a gunbattle that lasted several hours and killed several militants.

Pakistani Taliban spokesman Ahsanullah Ahsan claimed responsibility for the attack and denied that any militants were killed. He spoke to The Associated Press by telephone from an undisclosed location.

Associated Press writer Riaz Khan contributed to this report.