The helicopter went missing Friday en route from Pakistan to Turkmenistan, a journey that was to have taken it over Afghanistan's mountainous east and north, the International Committee of the Red Cross (ICRC) said.

The NATO peacekeeping force had dispatched "several" military helicopters and fixed-wing aircraft to search the mountainous border with Pakistan and with Turkmenistan, spokeswoman Annie Gibson-Sexton said.

The US-led coalition, which has been here for four years to hunt down militants from the ousted Taliban regime, also had aircraft involved in the search, spokesman Mike Cody said. He declined to give details.

The Mi-8 transport helicopter was chartered by the ICRC for relief operations in Pakistan after the October 8 earthquake that killed more than 73,000 people in northwestern Pakistan and Pakistani Kashmir.

It was carrying seven crew members from Turkmenistan.

Afghanistan's rugged and difficult terrain, notably the mountains in the east and north which have heavy snowfall in winter, is a serious challenge to pilots.

More than a dozen helicopters operating under NATO and coalition deployments have crashed or been shot down by insurgents since the forces started operations after the ousting of the Taliban regime in 2001.

In April last year an American Chinook helicopter crashed in bad weather in the southern province of Ghazni, killing all three civilians and 15 soldiers aboard.

It was the worst helicopter crash during US operations in Afghanistan.

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