A Russian military helicopter crashed in Chechnya on Friday, killing three crewmembers and 15 paratroopers on board, the Itar-Tass news agency reported, citing military sources.

"During an airlifting operation of paratroopers south of Shatoi, a helicopter Mi-8 has fallen down at 11:34 Moscow time (07:34 GMT) on Friday," Russian Air Force spokesperson Alexander Drobyshevsky was quoted as saying.

A team of investigators have arrived at the site to look into the cause of the crash, the spokesman said.

He said the incident might be caused by technical malfunction or shelling from the ground.

Russian news agencies, quoting military sources, said 18 people on board the helicopter had died.

They said the Mi-8 transport helicopter was shot down by Chechen rebels.

The downed helicopter was one of three carrying troops to take part in an operation against the insurgents near the town of Shatoi in southern Chechnya, RIA news agency quoted a source in the Russian regional military headquarters as saying.

The agency also said a gunfight was raging at the scene of the crash between insurgents and Russian forces.

Interfax news agency quoted a source in Chechnya's security forces as saying a senior insurgency leader could be among the rebels now fighting Russian troops at Shatoi.

The air force, in a statement, confirmed the aircraft had come down but said nothing about the cause .

Russia has been fighting in Chechnya since 1994, when then President Boris Yeltsin, who died this week, sent in troops to put down a separatist rebellion.

President Vladimir Putin vowed to squash the rebels when he took office seven years ago. Moscow's forces, working with local allies, have killed the main separatist leaders and driven the rebels into mountain hideouts.

The biggest loss of life sustained by Russian and pro-Moscow forces last year was when seven troops were killed during an operation near Shatoi.

(China Daily via agencies April 28, 2007)