US drones fired missiles at a compound and vehicle in a village in Pakistan's North Waziristan region on Monday, killing at least six militants, a senior security official told AFP.

"The identities of those killed in the strike is not yet known," the official said on condition of anonymity.

"There are still four drones flying over Datta Khel," he said.

A second security official confirmed the strike which took place in Sunzalai village near Datta Khel, a town 45 kilometres (28 miles) west of Miranshah, the main town in North Waziristan -- a renowned hot-bed of Taliban and Al-Qaeda linked militants.

In total six missiles were fired at the compound and vehicle, injuring another five militants, a local security official said, adding that the compound belongs to a local tribesman.

The United States considers the northwestern tribal region of Pakistan, which borders Afghanistan, a haven for Islamist militants who use the lawless area as a base to plan and carry out attacks on NATO and Pakistani forces.

The US has dramatically increased the frequency of drone strikes in the tribal belt in response to intelligence claims of a Mumbai-style terror plot to launch commando attacks on European cities.

More than 150 people have been killed 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 pilotless aircraft in the region.

Officials in Washington say drone strikes are highly effective in the war against Al-Qaeda and its Islamist allies, killing a number of high-value targets, including Pakistan's Taliban founding father Baitullah Mehsud.

But the policy is unpopular among the Pakistan public who see military action on Pakistani soil as a breach of national sovereignty.

It has led to reprisals from militant groups who have targeted NATO supply convoys destined for Afghanistan.

Gunmen on Monday led fresh attacks on NATO tankers in southwest Pakistan, torching vehicles carrying oil for the US-led war effort in Afghanistan, officials said.

Three tankers were attacked in Baluchistan, the province that borders Iran and Afghanistan and is suffering a regional insurgency as well as violence by Taliban.

The attacks came a week after Pakistan reopened the main land border crossing used by NATO supply convoys, following an 11-day closure imposed after a cross-border NATO helicopter strike killed two Pakistani soldiers.

"Four gunmen riding two motorbikes opened fire at two NATO oil tankers in the Mangochar area while they were on their way to Afghanistan," local police official Muhammad Ismail told AFP.