Gunmen downed the helicopter, killing 18 men, including three crewmembers, before escaping into the mountains after losing at least three of their own in a battle with security forces, local government and military sources have said.
"A group of gunmen was encircled in the forest three to four kilometers (two miles) from the village of Benoi," head of the Shatoisky District Zhamlain Khadashev said. He said three of them were killed.
A military source in the forces stationed in Chechnya later confirmed that several of the gunmen had been killed or wounded, but could not specify how many. The operation is ongoing, the source said.
Three helicopters carrying troops were sent to augment a federal task force fighting gunmen near the village of Shatoi, 30 miles south of the capital Grozny, earlier Friday.
One Mi-8 Hip transport helicopter was downed by automatic rifle fire as it approached the target area, killing everyone on board in what is apparently the second-deadliest attack on a federal helicopter in Chechnya in recent years, after the downing of a heavy Mi-26 Halo helicopter August 19, 2002, in which 127 on board were killed.