Moscow, Russia (CNN) -- An apparent accidental explosion rattled the nerves of residents in the southern Russian city of Vladikavkaz, in North Ossetia, on Saturday, just two days after a deadly attack at a city market, Russian media reported.
"A grenade has exploded, maybe as a result of reckless negligence," the RIA-Novosti news agency quoted Soslan Sikoev, the deputy head of North Ossetia's Internal Affairs Ministry, as saying.
Sikoev said the explosion was not a terrorist act, the news agency reported.
No casualties have been reported, according to RIA-Novosti.
The car in which the grenade exploded belongs to a military service member, the news agency reported.
Earlier, a police source told RIA-Novosti that the explosion was caused by a gas cylinder placed in a car.
The scene has been cordoned off while police and emergency officials work, RIA-Novosti reported.
Meanwhile, the death toll from Thursday's attack at the the central market in Vladikavkaz has risen to 18, according to the Itar-Tass news agency.
At least 123 people were wounded in that attack. Police believe a suicide bomber detonated an explosive device containing the equivalent of 40 kilograms of TNT inside a car.
The Investigative Committee of the Russian Prosecutor's Office called the attack a "terrorist act." The committee also said the bomb was stuffed with various pieces of metal to increase the human casualties. A natural gas canister, stored in the car's trunk, also detonated, the committee said.
The regional health ministry says 110 injured people remain in Vladikavkaz hospitals. Four are in grave condition. Eleven critically injured people were flown to Moscow overnight on a special Emergencies Ministry plane, according to Itar-Tass.
North Ossetia and the rest of the Caucasus region have been plagued with violence and political instability.
The market where the attacks occurred has seen other terrorist incidents in the past.
In November 2008, a suicide bomber blew up a bus at a nearby station, killing 12 people and wounding more than 40. And in March 1999, an explosion killed more than 50 people and wounded 300.