A US drone strike in Pakistan's northwestern tribal belt on Tuesday killed four militants, destroying their vehicle, local security officials said.

The strike took place in Spalga village, 15 kilometres (nine miles) south of Miranshah, the main town of the North Waziristan tribal district, near the Afghan border.

"It was a US drone strike, which targeted a militant's vehicle, killing four rebels," a senior local security official told AFP.

Another security official confirmed the strike and said the drone fired two missiles.

He said the nationalities of those killed in the strike were not immediately known.

Washington has dramatically escalated its drone campaign against militants in areas near the Afghan border over the past two months, and argues they are highly effective in the war against al-Qaeda and its Islamist allies.

More than 260 people have been killed in 51 strikes since September 3, heightening tensions with Islamabad over reported US criticism of Pakistan's failure so far to launch a ground offensive in North Waziristan.

The United States does not as a rule confirm drone attacks, but its military and the Central Intelligence Agency operating in Afghanistan are the only forces that deploy the aircraft in the region.

The US strikes are deeply unpopular among the Pakistani public, who see military action on Pakistani soil as a breach of national sovereignty and say some attacks have killed innocent civilians.

Washington says the strikes have killed a number of high-value targets, including the former Pakistani Taliban chief Baitullah Mehsud.

The US considers Pakistan's tribal belt an Al-Qaeda headquarters and the most dangerous place on Earth, and has reportedly criticised Pakistan's failure so far to launch a major ground offensive in the tribal region of North Waziristan.