A Russian military helicopter has crashed in the troubled southern republic of Chechnya, killing 18 people on board, Russian media report.
The Mi-8 has long been a Russian military workhorse (file pic)
The Mi-8 helicopter was involved in a major military operation against separatist rebels at the time, Russian military sources are quoted as saying.
Reports that the helicopter was shot down have not yet been confirmed.
The military operation, involving paratroops, took place in a mountainous area near the southern town of Shatoi.
A senior Russian military official in the North Caucasus told Interfax news agency that 15 paratroops and three crew members died in the crash.
Mi-8s have been widely used to transport troops during the long-running Chechnya conflict and are often targeted by rebels.
In August 2002 an Mi-26 transport helicopter packed with troops was shot down in Chechnya, killing 127 people.
It was the worst military aviation disaster since Russian forces stormed into Chechnya to crush a separatist revolt there in December 1994. A Chechen was jailed for life in 2004 for his role in the incident.
Russian forces resumed large-scale military operations in Chechnya in 1999, when Vladimir Putin was prime minister, but in recent years the fighting has been less intense than before.