UPDATE 2-Suicide bomber kills three police in Russian Caucasus

* Six in hospital, one person unaccounted for

* Suicide bomber struck at police check point (Adds Interior Ministry statement)

By Thomas Grove

MOSCOW, Feb 14 (Reuters) - A suicide bomber killed three policemen and wounded another six in Russia's North Caucasus on Thursday, hours before President Vladimir Putin was to meet with officials to discuss security ahead of next year's Winter Olympics.

The Kremlin is fighting to staunch an insurgency that aims to carve an Islamic state out of the Caucasus region, which borders Sochi, Russia's planned site for the 2014 Games.

The suicide bomber detonated explosives at a security checkpoint as police stopped his car for a routine document check on its way into the city of Khasavyurt in Dagestan province, the Interior Ministry said.

"Police officers stopped the...car for a (routine) check. Behind the wheel was a terrorist suicide bomber," the ministry statement said. "When police officers walked up to the car, he detonated the explosive device."

One person remained unaccounted for and six police were taken to hospital, officials said.

Rooted in two separatist wars in Chechnya, Islamist insurgents launch attacks daily as part of their campaign to turn the predominantly Muslim North Caucasus region into an Islamic state.

Dagestan, on the eastern edge of the Caucasus mountain chain, has emerged as the epicentre of violence.

It was unclear how many people were in the car, but the Interior Ministry said that the original target was likely in Khasavyurt.

Russian police are under orders to clamp down on insurgent violence across the North Caucasus ahead of the Sochi 2014 Winter Olympics. Putin told security officers last year to prevent attacks on the major events that Russia will host in coming years, including the 2018 World Cup.

Putin was to meet senior officials from the Federal Security Service, the domestic intelligence agency, on Thursday to outline their priorities for the year.

The Investigative Committee, a criminal investigation arm that answers only to Putin, said the explosion tore a hole almost four metres (13 feet) wide in the checkpoint building.

Television showed pictures of the twisted wreckage of the car near the security checkpoint where police regularly check identity papers.

Human rights groups say the insurgency, led by self-styled emir of the North Caucasus Doku Umarov, is being driven by a volatile mix of religion, corruption and grievances against the strong-arm tactics of some local leaders against suspected militants and their families.

The suicide bombing followed a police raid on a Dagestani forest hideout that killed five militants earlier this week. (Reporting by Thomas Grove; Editing by Jon Boyle)