At least six people were killed in a US drone strike on a militant compound in a northwestern Pakistani tribal area on Sunday, officials said.

The attack took place in Shawal , about 55 kilometres (35 miles) west of Miranshah, the main town in North Waziristan tribal district, along the Afghan border.

"US drones fired four missiles into a militant compound. At least six militants were killed and three others were wounded," a security official told AFP.

A second security official confirmed the attack and death toll.

The officials said the identities of those killed were not yet clear.

Pakistan's foreign ministry said it "strongly" condemned the drone attack.

"These unilateral strikes are a violation of Pakistan's sovereignty and territorial integrity. Pakistan has repeatedly emphasised the importance of bringing an immediate end to drone strikes," it said in a statement.

US drone attacks are deeply unpopular in Pakistan but Washington views them as a vital tool in the fight against Taliban and Al-Qaeda militants in the lawless tribal areas along the border with Afghanistan.

The Pakistani government has repeatedly protested against the strikes and there has been a recent decrease in their use.

During a visit to Islamabad at the start of August, US Secretary of State John Kerry suggested that drone strikes targeting Taliban and Al-Qaeda operatives in Pakistan could end "very soon" as the threat of militancy recedes.

According to an AFP tally there were 101 attacks in 2010, killing more than 670 people, compared with just 19 so far this year, killing just over 100 people.