A transport helicopter operated by the US-led NATO force has crashed in southern Afghanistan, and at least four people on board were killed.

A transport helicopter operated by the US-led NATO force has crashed in southern Afghanistan, and at least four people on board were killed.

The Western military alliance said that the aircraft, owned by the Kabul-based logistics company Supreme and crewed by four Tajik civilians, went down somewhere in the west of Zabul province, which is situated 340 kilometers (210 miles) south of Kabul, late on Saturday.

NATO also said that there had been no militant activity in the area at the time of the crash and the cause of the crash was being investigated.

On December 30, 2011, Taliban spokesman Yousef Ahmadi said that the group’s militants had shot down a CH-47 Chinook military helicopter flown by the US-led International Security Assistance Force (ISAF) in the Sayyad district of the northern province of Sar-e Pol.

However, Afghan officials dismissed the Taliban's claim, saying the helicopter had gone down due to a mechanical failure. They added that the pilot had sustained injuries.

On December 19, 2011, the Taliban said they had shot down a US helicopter in the southern province of Zabul as the aircraft was trying to rescue the crewmembers of another helicopter that had crashed nearby.

The rising number of casualties in Afghanistan has caused widespread anger in the US and other NATO member states, undermining public support for the Afghan war.

According to official figures released by the website icasualties.org, 37 foreign troops have lost their lives in Afghanistan so far this year.

Last year, 566 US-led soldiers were killed in Afghanistan. The year 2010, however, remains the deadliest year for foreign military casualties with a death toll of 711.