At least 17 people were killed when their troop-carrying helicopter was shot down in Russia's volatile province of Chechnya on Friday, Russian news agencies and the military said.

The incident appeared to be the deadliest single attack for over a year by Chechnya's insurgents. They have fought a 12-year war against Moscow's rule but in the past few years most of their leaders have been killed and their attacks curtailed.

A spokesman for the military prosecutor's office said: "According to our information, a helicopter came down as a result of which all those on board were killed, that was four crew and 13 troops."