A passenger train was derailed by a blast last night in Russia's southern Dagestan, the latest violence to hit regions bordering the rebel province of Chechnya, a local interior ministry official said.
No injuries were reported in the incident.
Itar-Tass news agency quoted local transport officials as saying unknown gunmen fired on a car from the FSB security service, wounding one officer who was on his way to the blast site. He was taken to a nearby hospital.
RIA Novosti news agency quoted a local official as saying unknown people had planted an explosive device on the tracks and it had exploded as the train passed.
Earlier this week, the second-highest ranking official in Ingushetia, also in Russia's Caucasus region and bordering Chechnya, narrowly escaped an assassination attempt which Russian authorities blamed on Chechen rebels.
The latest upsurge in violence comes just a week before the first anniversary of the school siege in Beslan in southern Russia by Chechen separatists which ended with 330 people dead, half of them children. That siege had been preceded days before by a string of attacks, including the blowing up of two domestic passenger planes by suicide bombers, killing almost 100 people.
A Chechen rebel website announced on Friday that the man behind the school siege, Shamil Basayev, had been appointed deputy leader of the separatist movement which Moscow has been battling for a decade.
Mr Basayev, Russia's most wanted man and self-described "bad guy", had been forced out of the movement's leadership in 2002 after then guerrilla leader Aslan Maskhadov said his methods were too extreme. Mr Maskhadov was killed by Russian forces in March and replaced by Muslim cleric Abdul-Khalim Sadulayev.
A number of analysts have said that with the death of the relatively moderate Maskhadov, the separatists would turn even more radical in their attempts to split predominantly Muslim Chechnya from the rest of Russia.
President Vladimir Putin, who came to power in 2000 on the back of a hardline approach to Chechen rebels, has refused to negotiate with them or recognise the rebel government.