Heavy fighting is taking place in the southern Caucasus after Russia responded to clashes between Georgian forces and separatists in South Ossetia.
Georgian President Mikheil Saakashvili will declare martial law in a few hours time, the secretary of Georgia's Security Council has said.
Background: South Ossetia
Conflict between Georgia and an increasingly assertive Russia has long been in the making and there is no certainty it will end quickly despite the enormous disparity of their forces
Russian aircraft have attacked a number of Georgian targets, including the Vaziani military airbase outside Tbilisi, and Moscow has since moved over 150 tanks and armoured vehicles into South Ossetia.
About 140 buses carrying refugees from South Ossetia have arrived in the adjacent Russian region of North Ossetia, with many more refugees expected to arrive on Saturday.
A senior Russian military commander confirmed that parts of Russia's 58th army are now on the outskirts of Tskhinvali, capital of the disputed territory.
Tskhinvali saw sustained clashes overnight as Georgia surrounded and shelled the city - leaving at least 15 civilians dead. Rebel leaders claim the actual civilian death toll is far higher.
The commander of Russian peacekeeping forces in the region said Tskhinvali has been 'almost totally destroyed' in the attack. It is understood at least 10 Russian troops were killed in the overnight barrage.
Speaking to CNN this afternoon, President Saakashvili stressed Russia was fighting a war with his country and said Georgians were 'looking with hope' to America, but he did not specifically appeal for US help.
'We have Russian tanks moving in. We have continuous Russian bombardment since yesterday...specifically targeting the civilian population.'
Georgia's National Security Council earlier warned that Moscow and Tbilisi would be in 'a state of war' if the reports of a Russian military convoy entering South Ossetia proved true.
President Saakashvili accused Russia of conducting a large scale military operation against his country. He has also ordered the mobilisation of Georgian military reservists.
Condemnation
The EU and the OSCE have led international calls for a ceasefire in South Ossetia - which broke away from Tbilisi's control in the early 1990s.
Russian President Dmitry Medvedev is currently discussing Moscow's next move with his advisors, while Prime Minister Vladimir Putin earlier warned that 'Georgian aggression' would incur a Russian response.
Russia is the main backer of South Ossetia's separatists, who have been trying to break away from Georgia since the early 1990s.
Conflicts between Georgia and South Ossetia and another breakaway republic, Abkhazia, began when the Soviet Union broke up almost two decades ago.
Violence has flared occasionally, but signs have increasingly pointed to a major showdown.
The UN Security Council has been unable to agree on a Russian-drafted statement calling for an end to fighting in the southern Caucasus.
Meeting in an emergency session in New York, the Council failed to reach consensus on a statement that would have called for an end to fighting between Georgian troops and separatists in the break away republic of South Ossetia.
Envoys are being sent from the US and the EU to the region in a bid to broker a ceasefire, though it is unclear at present who they will meet with once arriving in Georgia.
