The Georgian foreign ministry has said Russia took a "step toward the de-facto annexation" of Georgia's breakaway territory after Moscow has signed a deal with Abkhazia, giving greater military control over Black Sea region.
Under the treaty signed on Monday by Russian President Vladimir Putin and Abkhazia's leader Raul Khadzhimba, Russian and Abkhazian forces in the territory will turn into a joint force led by a Russian commander.
The move raised further suspicions in the West about Russian President Vladimir Putin's territorial aspirations after his annexation of Ukraine's Black Sea peninsula of Crimea in March.
"I'm sure that cooperation, unity and strategic partnership between Russia and Abkhazia will continue to strengthen," said Putin.
Russian troops have been deployed in Abkhazia for more than two decades since the region of 240,000 people broke away from Georgia in a separatist war in the early 1990s.
Still, Monday's agreement reflected a clear attempt by Moscow to further expand its presence and came only after a change of leadership in the territory.
Abkhazia's former leader, Alexander Ankvab, was forced to step down earlier this year under pressure from protesters who reportedly were encouraged by the Kremlin. Khadzhimba, a former Soviet KGB officer, was elected president in an early vote in August that Georgia rejected as illegal.
Unlike Ankvab, who had resisted Moscow's push to let Russians buy assets in Abkhazia, Khadzhimba has appeared more eager to listen to Russia's demands.
"Ties with Russia offer us full security guarantees and broad opportunities for socio-economic development,'' said Khadzhimba.
Georgia called on the international community to condemn Russia's move.
Russian-Georgian relations were strained by war in August 2008 after former Georgian President Mikhail Saakashvili attempted to restore control over another breakaway province, South Ossetia. The Russian military routed the Georgian forces in five days and Moscow recognised both rebel provinces as independent states.