Russia sent troops from breakaway Abkhazia deep into Georgia this afternoon, opening what amounted to a second front, having forced Georgian troops to withdraw from the capital of South Ossetia.
The Russian Defence Ministry justified the operation in Senaki, which lies outside the so-called security zone along the de facto Abkhaz boundary, by the need to avert new attacks on South Ossetia.
"Russian peacekeepers and support units are carrying out an operation aimed at preventing the shelling of peacekeeping forces by Georgian artillery and aimed at preventing Georgian forces from regrouping to carry new attacks on South Ossetia," a ministry spokesman said.
"Senaki is one of the places where such actions were under way," he said. Senaki lies some 25 miles from the boundary with Abkhazia.
Russian peacekeepers have been based inside Abkhazia and within a "security zone" running along the boundary since the early 1990s, when Abkhazia fought to throw off Georgian rule.
Russia now has more than 9,000 paratroopers and 350 pieces of armour in the separatist region, having poured in troops while fighting Georgian forces in the country's other breakaway territory of South Ossetia.
"They have advanced in dozens of armoured personnel carriers and are now in Senaki," said Georgian Interior Ministry spokesman Shota Utiashvili.
The development will deepen Western concern about a second front opening in Russia's conflict with Georgia, after days of intense fighting between Russian and Georgian forces for control of the South Ossetian capital Tskhinvali.
Georgia says it has pulled out of Tskhinvali and ceased fire. But Russia said Tskhinvali had come under heavy shelling on Monday from Georgian positions.
Georgia said earlier that Russian troops had entered the town of Zugdidi, inside the Abkhaz security zone, and issued an ultimatum to Georgian forces to disarm or face attack.
Interfax news agency quoted the head of the Russian peacekeeping force in Abkhazia, Sergei Chaban, as saying Russian forces were nearly ready for an operation to disarm Georgian troops in the area.
"If the ultimatum is rejected all necessary enforcement measures will be used," Chaban said.
A Georgian Interior Ministry spokesman replied: "We are not going to surrender any arms to the Russians."
The simmering conflict between Russia and its small, former Soviet neighbour erupted last Thursday when Georgia suddenly sent forces to retake South Ossetia, a pro-Russian province that threw off Georgian rule in the 1990s.
Moscow responded with a counter-attack that drove Georgian forces out of the devastated South Ossetian capital Tshkhinvali yesterday. Russia says more than 2,000 people have been killed in the fighting and thousands more are homeless but these figures have not been independently verified.
Mr Saakashvili told reporters on a conference call that Russia "wants to replace the government in Tbilisi" and claimed that Moscow wanted to seize control of energy routes in the region.
However, Moscow insisted it had not moved its troops beyond the territory of South Ossetia and a second separatist region, Abkhazia, and had no intention of pushing further into Georgia.
President Dmitry Medvedev said the operation to restore calm in South Ossetia was nearing its conclusion and the Russian General Staff said at a military briefing that staying within the borders of South Ossetia was a "key principle".
Despite international calls for peace, both sides continued to fight today. Georgia shelled Tshkhinvali early in the day despite declaring a ceasefire yesterday, and Tbilisi said Russian jets had bombed Georgian targets again overnight.
Russia said at a daily military briefing that it had lost four military aircraft and 18 soldiers since the fighting started, with another 14 missing in action and 52 wounded.
But Colonel-General Anatoly Nogovitsyn rejected out of hand Georgian claims that up to 50 Russian jets had bombed Georgia overnight.
"Fifty ? Is that what they said ? How do they count them at night ?," he said. "We don't do that. We don't have 50 planes flying at night."
Reuters