© UnknownThe US has conducted another unauthorized drone airstrike in Pakistan's troubled northwest, leaving at least 23 people dead and several others wounded.
Officials say the US drones have fired five missiles into North Waziristan close to the Afghan border.

Meanwhile, Pakistani medics reported that the missiles fired by US drones have contaminated the environment with unknown chemicals.

They say most of those wounded by US drone airstrikes in North Waziristan are hospitalized for various skin, eye and respiratory diseases caused by chemicals.

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 non-UN-sanctioned US strikes.

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

Attacks by unmanned American planes have left dozens of people dead in the volatile region over the past weeks.

The aerial attacks, initiated by former US president George W. Bush, have been escalated under President Barack Obama.

Islamabad has repeatedly condemned the attacks, saying they violate Pakistan's sovereignty.

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 "play station" mentality.