Unmanned US aircraft fired four missiles at a house in north-west Pakistan today, killing 16 suspected militants, Pakistani intelligence officials said.
The strike prompted a swift condemnation by the Pakistani government, which released a statement saying the strikes are a violation of its sovereignty.
The strike in the Sarai Darpa Khel area of the North Waziristan tribal region also wounded two suspected militants, said the officials.
The suspected militants who were targeted were believed to be from the Afghan Haqqani network. US officials consider the Haqqani network to be one of the most dangerous militant factions fighting American troops in neighbouring Afghanistan. The leadership of the network pledges allegiance to Taliban chief Mullah Omar but operates fairly independently.
US 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.
"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.
US officials rarely provide details publicly about the covert CIA drone program in Pakistan.
Elsewhere in north-west Pakistan, militants attacked a police post before dawn and killed six policemen, said a local government administrator, Habibullah Khan.
Ten officers were wounded in the attack about 15 miles south east of the city of Peshawar, said another government official, Feroz Shah. The post was staffed by paramilitary police from the Frontier Constabulary force and also by tribal policemen.
Mr Khan said police retaliated in a gun battle that lasted several hours and killed several militants.
No one has claimed the attack, but the Pakistani Taliban has carried out many similar attacks against security personnel in the area.