"Heavy fighting in and around Tskhinvali is ongoing," the South Ossetian Press and Information Committee reported. "The people of South Ossetia request the president and the leadership of the Russian Federation to help and to undertake measures to protect its citizens."

Most residents in South Ossetia and Georgia's other breakaway region have been issued Russian passports as Moscow stepped up ties with the rebel governments in recent years, angering Tbilisi.

Over 2,500 Russian peacekeeping troops have been patrolling the two breakaway provinces since a UN ceasefire agreement ended a bloody civil war in 1994.

President Dmitry Medvedev was holding consultations with his top aides to plan Moscow's response, the Kremlin press office said Friday.

"A series of measures is now being discussed under the guidance of Dmitry Medvedev, aimed at restoring peace in South Ossetia, and defending the local civilian population within the peacekeeping mandate we have," it said.

"The president is constantly receiving full information from the scene of military actions in South Ossetia," the Kremlin said in a statement posted on its website.

Russian Premier Vladimir Putin held talks Friday with US President George W Bush, who is Georgia's closest ally.

Putin, in Beijing for the Olympic games opening ceremony, condemned "aggressive actions" by Georgian troops in South Ossetia, and said that Russia would be compelled to retaliate.

In April this year, NATO leaders pledged that Georgia would join the alliance at an unspecified future date. Since then, tensions have escalated, with Russia shooting down an unmanned Georgian drone over Abkhazia and deciding to strengthen diplomatic ties with the region.