As many as 20 people are reported to have been killed and 100 more wounded when two powerful blasts hit a police post outside the capital of Russia's violence-plagued Dagestan region.
The first explosion occurred when police stopped a vehicle for document checks late on Thursday, RIA news agency reported, citing a statement by the National Anti-Terrorist Committee.
A second bomb exploded when fire brigades and ambulances arrived, causing additional casualties.
A law enforcement source cited by the agency said up to 20 people were dead and 30 wounded, while the Lifenews website, quoting a local police official, reported 17 people dead and 68 injured.
"Fragments of human bodies are scattered at the post," Interfax quoted a law enforcement official as saying.
The unofficial Islamist website www.kavkazcenter.com said the police post was almost destroyed.
A nearby gas pipeline also was damaged during the attack, RIA reported.
Dagestan, with its capital Makhachkala, has been caught up in an insurgency across the mainly Muslim North Caucasus following two separatist wars in Chechnya.
The rebels want to create an Islamic state in the region, which is close to Sochi, where Russia will host the winter Olympics in 2014.