The explosion occurred in the early hours of Saturday morning, according to news reports. There were no reported injuries.

The blast, which according to preliminary information was due to an explosive device planted underneath a 5000-tonne oil cistern, occurred at 03:00 Moscow time (23:00 GMT) on Friday, emergency officials said as quoted by the ITAR-TASS news agency.

Another explosive device was reportedly found under another cistern, and the police were trying to disarm it, sources quoted by RIA-Novosti said.

There were no casualties, officials said.

Stavropol region borders the volatile Caucasus, including the war-torn republic of Chechnya.

Market toll rises

Meanwhile, the death toll in a bombing at an outdoor market in central Russia rose to 10 on Saturday, officials said.

The explosion ripped through the market in the Volga River city of Samara on Friday when it was packed with customers, instantly killing eight people and wounding dozens of others.

There has been no claim for
responsibility for the blast

Officials in Samara, a big industrial city some 800km southeast of Moscow, initially blamed the explosion on a leaky gas canister, but later said it was caused by a bomb.

Two other victims later have died at a hospital, bringing the death toll to 10, said a spokesman for the local branch of Russia's Emergency Situations Ministry who asked not be named. Another 38 people have remained hospitalised, some in grave condition.

There was no immediate claim of responsibility for the blast in Samara, Russia's sixth-biggest city, or indications of whether it was connected to separatist conflict or one of the commercial disputes that often turn violent in Russia.

The plastic explosive was placed on the back wall of one of the kiosks near a railway that ran alongside the market, officials said.