The US has conducted another non-UN-sanctioned drone strike in Pakistan's troubled northwest, leaving at least eight people dead and several others wounded.

The US drone hit a vehicle in South Waziristan region, which borders Afghanistan.

The US has expanded its airstrikes in Pakistan since President Barack Obama took office in 2009.

The US often carries out such attacks on Pakistan's tribal regions, claiming that the militants are their target.

But locals say civilians are the main victims of the unauthorized US strikes. Hundreds of people have been killed in the attacks.

There have also been numerous demonstrations across Pakistan against the US drone attacks.

The issue of civilian casualties has strained relations between Islamabad and Washington with the Pakistani government repeatedly objecting to the attacks.

The United Nations says the US-operated drone strikes in Pakistan pose a growing challenge to the international rule of law.

Philip Alston, UN special envoy on extrajudicial killings, said in a report in late October 2010 that the attacks were undermining the rules designed to protect the right of life.

Alston also said he fears that the drone killings by the US Central Intelligence Agency could develop a "playstation" mentality.