A Russian military helicopter crashed in Chechnya on Friday, killing all 18 people aboard, emergency officials said. There were conflicting reports about whether the craft was shot down.

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, speaking on condition of anonymity because he was not authorized to give his name to the media.

He said preliminary indications were that the helicopter — carrying 15 paratroopers 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.

A Russian air force spokesman in Moscow confirmed that a helicopter crashed in Chechnya, but declined to give details.

The loss of life would be the largest for Russian forces in a single incident in many months in Chechnya, the site of two devastating wars since 1994 pitting federal forces against separatist rebels.

Major offensives and large-scale fighting have all but ended, but militants continue to stage small hit-and-run ambushes with booby traps and remote-detonated explosives, mostly targeting Russian troops and forces of the Moscow-backed Chechen government.

The emergency official said the helicopter was one of three that was flying toward an area in southern Chechnya where a group of suspected militants had been spotted. The ITAR-Tass news agency quoted an unidentified law enforcement official as saying three militants were believed to have been killed in fighting in the area.