A US drone strike targeting a vehicle in Pakistan's northwestern tribal belt killed at least three militants on Saturday, security officials said, the latest in a recent spate of attacks.

This file photo shows a Pakistani soldier standing guard at a checkpost near Wana, the main town of South Waziristan. A US drone strike, targeting a vehicle in the area, killed at least three militants on Saturday, security officials said, the latest in a recent spate of attacks.

The strike -- the sixth in 11 days -- took place in Khawashi Khel village, five kilometres (three miles) west of Wana, the main town in the South Waziristan tribal district which borders Afghanistan, a Pakistani security official told AFP on condition of anonymity.

"The US drone fired two missiles which completely destroyed the vehicle. At least three militants have been killed," the security official said.

Another official said the attack took place as militants were trying to move from one area to another near the border.

Washington considers Pakistan's semi-autonomous northwestern tribal belt the main hub of Taliban and Al-Qaeda militants plotting attacks on the West and in Afghanistan.

Pakistani-US relations went into freefall last year.

There were hit when a CIA contractor shot dead two Pakistanis and dented further by an American raid that killed Al-Qaeda chief Osama bin Laden and by US air strikes in November that killed 24 Pakistani soldiers.

After the air strikes, Pakistan shut its Afghan border to NATO supplies and ordered US staff out of an air base reportedly used as a hub for drones.

Six US drone strikes have been reported since last month's NATO summit in Chicago, which failed to secure a deal on resuming the supply lines.

In March, parliament agreed to reset US relations but on condition that Washington apologise for the soldiers' deaths and end drone attacks on its soil.

Pakistan has been incensed by Washington's refusal to apologise for the November air strikes and US officials have so far rejected Pakistani proposals to charge several thousand dollars for each alliance truck crossing the border.

Islamabad, which is understood to have given its tacit approval for the attacks on Al-Qaeda and Taliban targets in the past, has become increasingly vocal in its opposition to the perceived violation of national sovereignty.

Despite Pakistani criticism US officials are believed to consider the drone attacks too useful to stop them altogether. They have argued that drone strikes are a valuable weapon in the war against Al-Qaeda and other Islamist militants.

According to an AFP tally, 45 US missile strikes were reported in Pakistan's tribal belt in 2009, the year US President Barack Obama took office, 101 in 2010 and 64 in 2011.

The New America Foundation think-tank in Washington says drone strikes have killed between 1,715 and 2,680 people in Pakistan in the past eight years.