"The Georgian authorities have unleashed a dirty war," the ministry said on its website, echoing statements from Russian officials and lawmakers who have condemned the ongoing Georgian ground and air offensive, which has killed several people including Russian peacekeepers.
"Bloodshed in South Ossetia will be on their conscience. We will protect our peacekeepers and citizens of the Russian Federation," the ministry said.
Georgia launched a major offensive overnight in its breakaway republic, where many people hold Russian passports, using tanks, combat aircraft, heavy artillery and infantry. Georgia says it has captured most of the region, and has called on the separatist authorities to surrender. (PHOTOS)
South Ossetia earlier said at least 15 civilians had been killed, and Russian peacekeepers said Georgia had shelled their positions, killing and wounding several Russian servicemen in the regional capital, Tskhinvali.
Georgia's pro-Western president, Mikheil Saakashvili, announced a full mobilization in the country. He also accused Russia of bombing Georgian villages, a claim Moscow swiftly rejected.
NATO, the European Union and the United States, a key ally of Georgia, all issued statements urging the sides to bring an end to the conflict.
Georgia's Rustavi-2 television said government troops had shot down a Russian military plane over Georgian airspace on Friday. The channel said several Russian planes had earlier dropped bombs on the town of Gori, to the south of South Ossetia.
Russia's Foreign Ministry dismissed the report as "mere ravings, another vile provocation by the Georgian authorities." The Defense Ministry called the report an "information provocation," and said no Russian aircraft had been downed.
Russian Prime Minister Vladimir Putin, speaking in Beijing, hinted at a Russian retaliation, saying Georgia's aggression would provoke a "response." Several senior lawmakers called for military action against Tbilisi.
"Russia must intervene in the conflict to end the violence," influential MP Konstantin Zatulin said. "Russia must consider the military operation because our peacekeeping contingent will not be sufficient to ensure peace in the region."
Saakashvili, who seeks NATO membership for Georgia, has pledged to bring South Ossetia, home to around 80,000 people, along with breakaway Abkhazia, back under central control, and has accused Russia of trying to annex the regions.