At least 30 people were injured after a car exploded in the centre of the southern Russian city of Pyatigorsk on Tuesday, a local emergencies department source said.
"Three of the wounded are in a critical condition," the source said.
An explosive device was detonated in a Lada car parked near a cafe at 16:15 Moscow time (12:15 GMT).
A criminal case has been launched on charges of terrorism, said a spokesman for the Russian investigations committee said.
President Dmitry Medvedev ordered the head of the Russian Federal Security Service (FSB) to do everything possible to get to the bottom of the incident.
Pyatigorsk is the capital of Russia's North Caucasus Federal District, which includes the volatile republics of Chechnya, Dagestan and Ingushetia, where terrorist attacks and militant clashes are common.
PYATIGORSK, August (RIA Novosti)