Islamabad, June 2 (RHC)-- At least four people have been killed in a fresh U.S. drone strike in Pakistan's volatile North Waziristan tribal area near the Afghan border.

According to sources, the strike took place when the assassination drone fired two missiles at a vehicle in the Shawal area of North Waziristan late on Monday. The car was completely destroyed in the strike, leaving the four dead.

On May 18th, another U.S. drone attack claimed the lives of at least three people in Pakistan's northwestern tribal region. A similar attack killed four people in the Warokey Mandi area of North Waziristan, where the Pakistani military forces have been operating against pro-Taliban and al-Qaeda-linked militants since last June.

The U.S. regularly uses drones for airstrikes and spying missions in Afghanistan, as well as in Pakistan's northwestern tribal belt, among other places. Washington claims that the targets of the drone attacks are militants, but local officials and witnesses maintain that civilians have been the main victims of the attacks over the past few years.

The aerial attacks, initiated by former U.S. President George W. Bush, have been escalated under President Barack Obama, who has defended the use of the controversial drones as "self-defense."

The United Nations says the U.S. drone attacks are "targeted killings" that violate international law.