A suicide car bomb attack on a busy marketplace in the Russian city Vladikavkaz, capital of North Ossetia, left at least 16 people dead on Thursday, dpa reported according to the Itar-Tass news agency.
Around 100 people were injured when the car packed with 40 kilogrammes of TNT exploded, according to the Interior Ministry in the mainly Christian region of North Ossetia.
Two persons were in the car, which bore the licence plates of the neighbouring predominantly Muslim republic of Ingushetia. The news agency Ria Novosti said the car owner was arrested.
The attack, which occurred on the final day of the Muslim fasting month of Ramadan, damaged numerous buildings in the city and set dozens of cars on fire.
Some reports put the death toll at 22. The Ministry for Emergency Situations sent two planes to North Ossetia to fly some of the badly injured to Moscow for treatment.
Russian President Dmitry Medvedev and Prime Minister Vladimir Putin condemned the attack and called on the region's Muslim population to help prevent similar incidents in the future.
Russia would do everything in its power to find the "monsters" behind the attack, said Medvedev. "If they resist they will be destroyed," he said.
Security precautions were increased across the country after the blast, with authorities evacuating all schools and kindergartens in North Ossetia, which borders on Georgia.
Six years ago, Islamist separatists carried out one of their worst attacks in Beslan, North Ossetia, in which more than 330 people were killed - including 168 children.
The neighbouring republics of Dagestan and Chechnya have seen repeated attacks by the separatists.
Medvedev ordered his special envoy for the northern Caucasus, Alexander Kloponin, to travel to Vladikavkaz. Police in the city defused a second bomb at the entrance to the marketplace, after the first one went off.
Putin accused the terrorists behind the car bombing of seeking to sow discord.
"We are counting on the Muslim population to make a decisive contribution towards the fight( against terrorism), Putin said.
Islamic separatist in the Muslim north Caucasus are fighting elements loyal to the Kremlin with the goal of setting up an independent "Caucasus Emirate" in the region.