Islamabad:  US drones, breaking an undeclared lull, on Wednesday resumed their campaign over Pakistan's tribal territory carrying out a strike that killed four militants.

The drones fired two missiles at a militant compound in Miranshah, the main town of North Waziristan Agency.

The attack was the first since November last year after media reports have said that the attacks had been suspended to avoid worsening relations between Washington and Islamabad after the deadly November 26 NATO raid that killed 24 Pakistani soldiers.

The missiles set the building on fire and flames could be seen from the roof of houses in Miranshah, which lies five kilometres from the targeted area.

Reports said that it was unclear if the attack presages a new round of strikes on Taliban and al-Qaeda-linked militants based in the remote tribal territory bordering Afghanistan.

The Los Angeles Times reported last month that the CIA had frozen drone strikes on gatherings of low ranking militants, but quoted officials as saying that the strikes would be undertaken if high value targets were spotted.

But, the identity of the four persons killed in the attack could not immediately be ascertained. It was also not known if the targeted persons were Taliban or foreign militants.

November strike by NATO helicopters triggered an outrage in Pakistan and aggravated tensions in an already shaky relationship with Washington, prompting Islamabad to block NATO supplies into Afghanistan and forcing the US to vacate Shamsi airbase, reportedly used by CIA-operated drones.

The US drone campaign has reportedly killed dozens of top al-Qaeda operatives and hundreds of low-ranking fighters in Pakistan since the campaign started in 2004.