A car bomb killed three people in the southern Russian city of Pyatigorsk on Friday, officials said, in a worrying development for the Kremlin as Russia prepares to host the 2014 Winter Olympics in Sochi in six weeks' time.

Pyatigorsk lies 270 kilometres east of Sochi, where the Games, a major prestige project for President Vladimir Putin, will open on Feb. 7.

The blast blew out the windows of buildings in an industrial neighbourhood of the spa resort town, officials said. Three people were killed, Pyatigorsk mayor Lev Travnev said on state-run Rossiya-24 television.

Pyatigorsk

Officials say the blast badly damaged a traffic police building and blew out the windows of buildings in the vicinity. (Google map)

Interfax said the blast badly damaged a traffic police building. The explosion blew out the windows of buildings in the area, a regional police spokesman, Yevgeny Arnautov, said on Rossiya-24 television. He gave no casualty figure.

The spa resort town of Pyatigorsk lies 270 kilometres east of Sochi, just north of a strip of mostly Muslim provinces plagued by near-daily violence linked to an Islamist insurgency whose leader has called on militants to stop the Games taking place.

President Vladimir Putin has ordered law enforcement agencies to improve security in the region as Russia prepares to host the Olympics in February in Sochi, at the northwestern edge of the Caucasus range.

Prevent the Olympics, says Chechen warlord

In a video posted online in July, the leader of the insurgency, Chechen warlord Doku Umarov, urged militants to use "maximum force" to prevent Putin staging the Olympics.

Militants say they want to carve out a Muslim state in the North Caucasus. Their insurgency is rooted in two post-Soviet separatist wars in Chechnya, one of the region's provinces.

Putin, who was first elected president in 2000 after launching the second war, which drove Chechen separatists from power, has staked his reputation on a safe and successful Games.

Nobody immediately was blamed or claimed responsibility for the bombing in Pyatigorsk. Militants based in the North Caucasus have carried out some of their deadliest attacks beyond its borders, in the Russian heartland.

Suicide bombers killed 40 people in the Moscow subway in 2010 and 37 at the Russian capital's busiest airport in 2011. A suicide bomber killed six people in October on a bus in the southern city of Volgograd.