A homicide bomber blew himself up in a truck at a traffic police checkpoint in Russia's volatile Ingushetia region, Russian agencies told Reuters on Friday.
Russia's Itar-Tass news agency, quoting the source to Reuters, said policemen were killed in the attack, but did not say how many.
The attack took place in the region's main city of Nazran, Interfax told Reuters.
A string of homicide bombs and armed attacks on Russian security forces in Chechnya, where the country has fought two separatist wars, and neighbouring Ingushetia and Dagestan, have shattered a few years of relative calm in the North Caucasus, where the Islamist insurgency has struggled against Russian authorities.
Regional leaders have warned Russian President Dmitry Medvedev that Chechen insurgents have infiltrated all spheres of society, making it difficult to contain them.