Russian President Dmitry Medvedev has ordered security to be tightened in South Ossetia, where eight Russian soldiers were killed in an explosion.
The soldiers died on Friday when a car blew up near a Russian military base in the regional capital, Tskhinvali.
A senior Russian officer was among those killed, Moscow said, blaming Georgian secret services for the blast.
Georgia has denied the charge, saying the blast was engineered by Russia to delay withdrawing troops from Georgia.
Tension remains high in the region following the conflict between Russia and Georgia over the summer.
Russian troops continue to occupy buffer zones around two breakaway Georgian regions - South Ossetia and Abkhazia.
The Russian-backed administration of South Ossetia said on Saturday that the death toll from the explosion was 11 - the eight Russian soldiers, and three civilians.
The Russian military said the chief-of-staff of what Russia calls its peacekeeping forces in the region, Colonel Ivan Petrik, was killed in the explosion.
President Medvedev had ordered a "painstaking investigation" into the explosion and ordered security forces in the region to take "all necessary steps to prevent criminal acts against Russian peacekeepers and the civilian population," a Kremlin statement said.
A spokesman for Russia's prosecutor-general's office said Georgian forces were behind the car blast.
The spokesman, Vladimir Markin, said there was "every reason to believe the explosion in Tskhinvali was arranged by Georgian secret services and is aimed at Russian peacekeepers to destabilise the situation".
Georgia's interior ministry denied the charge and suggested the explosion was part of a Russian plan to delay their withdrawal from the buffer zones, due to be complete by 10 October under a deal mediated by French President Nicolas Sarkozy.
According to a statement from the South Ossetian breakaway administration, Russian troops had confiscated the vehicle that blew up from an ethnic Georgian village because it was carrying weapons.
Fighting broke out between Russian and Georgian forces on 7 August when Georgia tried to retake South Ossetia by force.
Russia launched a counter-attack and the Georgian troops were ejected from South Ossetia and another region, Abkhazia, several days later.
Last week, European Union monitors entered the buffer zone around South Ossetia as part of the French-brokered peace deal.
Russia has recognised the two breakaway regions as independent and says it will keep nearly 8,000 troops in the two areas.
The EU wants its observers to have access to the breakaway regions, but Russia has repeatedly refused to guarantee that.