A suspected bomb blast killed 11 people outside a Russian market, prosecutors said, in one of the worst attacks in months to hit Russia's turbulent North Caucasus region.
The explosion detonated as a minibus taxi pulled up outside the main market in the southern Russian city of Vladikavkaz, killing passengers and ripping the doors off one side of the vehicle.
The attack was fresh evidence that despite largely quelling a separatist rebellion in nearby Chechnya, Russia is still struggling to contain violence in its southern regions that has fuelled instability and killed thousands of people.
Authorities say the explosion may have been carried out by a suicide bomber.
Russian President Dmitry Medvedev ordered police and state security agencies to tighten security and to keep him informed about the investigation.
Vladikavkaz is in Russia's North Ossetia region, scene of the Beslan siege in 2004 in which more than 300 people were killed after their school was taken hostage by gunmen linked to a separatist rebellion in Chechnya.
North Ossetia has tense relations with the neighbouring Russian region of Ingushetia that stem from an outbreak of sectarian violence in 1992 in which hundreds were killed.
North Ossetia has a mainly Christian population. It shares a border and a common ethnic identity with the Georgian separatist region of South Ossetia, which was the focus of a brief war between Moscow and Tbilisi in August.