At least eight people were killed Monday when a U.S. drone targeted the South Waziristan tribal area in northwest Pakistan, local sources said.

The pilotless aircraft fired four missiles at a vehicle in Wana, the main town in South Waziristan which borders Afghanistan, they said.

The identities of the killed are not immediately known, but Washington often claims the U.S. drone strikes aim to hit militant hideouts in Pakistan's mountainous tribal belt.

So far this year, the U.S. drones have carried out almost 40 attacks in Pakistan's northwest region, reportedly killing over 300 people.

While most of the people targeted by U.S. drones in Pakistan are believed to be militants who often launch attacks on the U.S.- led NATO troops in Afghanistan across the border, U.S. drones do often mistakenly kill innocent civilians, leading to repeated protests by the local people and the Pakistani government as well.