Russia ? A Russian military helicopter heading to a battle with separatist rebels crashed Friday in Chechnya, killing all 18 people aboard, emergency officials said.

There were conflicting reports about whether the craft was shot down, but the crash en route to a military operation underlined the persistence of Chechnya’s insurgency years after the most recent major fighting.

It was the largest single-day loss of life reported by the Russian military in Chechnya in at least two years.

The Mi-8 helicopter went down while flying to southern Chechnya as part of an operation against militants, an official at the regional branch of the Emergency Situations Ministry said.

The emergency official said preliminary indications were that the helicopter – carrying 15 soldiers and a crew of three – was shot down, but a ministry duty officer in the region later called the crash an accident, saying a rotor blade had struck something during an attempt to land.