A police post in the village of Ubiat came under fire from guns and grenade-launchers, the spokesman said.

Russia accused Tbilisi of carrying out an "act of aggression" against South Ossetia, while the EU and the Organization for Security and Cooperation in Europe expressed concern over the heaviest fighting in the volatile region so far this year.

Russian President Dmitry Medvedev urged Georgian President Mikheil Saakashvili on June 5 to refrain from "stoking tensions" in Georgia's breakaway regions.

The Ossetian separatists threatened to retaliate with heavy weapons after Georgian forces fired mortars and rocket propelled grenades at the capital, Tskhinvali, late on Thursday killing two people. Earlier this week, several people were injured in a bomb blast in Abkhazia. The separatists there blamed the blast on Tbilisi and said the region would seal itself off from Georgian-controlled territory.

Russia has said it will use weapons to "defend compatriots" in Abkhazia and South Ossetia if Georgia launched a military action against the separatists.