A Russian helicopter has crashed near the Chechen capital Grozny killing all four people on board, after reportedly coming under rebel fire.

The Interfax news agency quoted a Russian Interior Ministry official as saying the Mi-8 helicopter crashed as it attempted to land, at around the same time as a mobile anti-aircraft missile was fired in the area.

The helicopter was said to have crashed 30 metres off the ground near Russia's main military base in the region at Khankala.

Eyewitnesses say that the helicopter spun on its axis for some time after being hit and then dropped to the ground and exploded.

Three of the dead are thought to be crew members, while the fourth was a military officer accompanying cargo.

Putin's promise

The incident comes as Russia is launching a crackdown in the republic following the seizing of hundreds of hostages last week in Moscow by a group of heavily armed Chechens.

After Russian forces stormed the building and more than 100 of the hostages died, President Vladimir Putin promised the army would wipe out what he called "terrorist bases" at home and abroad.

One report said around 100 suspected militants had been detained in Chechnya in the past 24 hours.

But the BBC's Jonathan Charles in Moscow says this latest downing of a helicopter shows just how difficult it is for the Russian army to beat the tough Chechen fighters.

Rebels have shot down several Russian helicopters in the republic, most recently in August when a Mi-26 packed with troops was downed in the same area. More than 100 people were killed.

Mi-8s are usually used as gunships in the conflict area and are often targeted by rebels.