Georgian Railway spokeswoman Irma Stepnadze told AFP that no one was injured in the blast, which damaged 100 metres (yards) of track and overturned 16 wagons.

“According to preliminary information, TNT was used in the explosion,” she said.

The blast happened in the early morning on the line between Senaki and Georgia’s Black Sea port of Poti, a major centre for oil exports.

Georgia is part of a key transport corridor carrying oil and gas from the Caspian Sea to Western markets.

Stepnadze said repair work was underway but it was unclear when traffic on the line would resume.

The railway network in western Georgia has been hit by three bomb blasts in recent months, including explosions at the central train station in the western city of Zugdidi in June. No one has been seriously injured in the blasts.

Officials have described some of the blasts as “terrorist acts” and suggested that rebels in the breakaway region of Abkhazia were behind the attacks.

Tensions remain high around Abkhazia and another Georgian rebel region, South Ossetia, following last year’s Georgia-Russia war over the breakaway provinces.

Russia sent troops and tanks into Georgia in August 2008 to repel a Georgian military attempt to retake South Ossetia. Russian forces later withdrew inside the rebel regions, which Moscow recognised as independent states.