LONDON, April 28 (Reuters) - Moody's cut the outlook on Georgia's sovereign BA2 credit rating to negative from stable on Thursday, warning of risks linked to Russia's invasion of Ukraine and Tbilisi's own history of clashes with Moscow.

The rating agency said the decision to change Georgia's outlook - which effectively puts it on a downgrade warning - reflected the "heightened geopolitical event risks" given Georgia's "frozen" conflicts with Russia over South Ossetia and Abkhazia.

"While not Moody's base case, a crystallization of these political risks, including a possible expansion of the military conflict to Georgia and a consequent significant and sustained impact on Georgia's economic and fiscal prospects, would weigh on its credit outlook," Moody's said.

Moscow recognised the breakaway regions of South Ossetia and Abkhazia as independent after fighting a war with Georgia in 2008. It stationed thousands of troops in both regions and has provided them with extensive financial support.

The presence of Russian troops "increases the risk of the military conflict in Ukraine spilling over into Georgia", Moody's said.

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South Ossetia said last month it would hold a referendum in the near future on becoming part of Russia, a plan Georgia said was unacceptable.

The United States and other Western nations continue to regard both South Ossetia and the Black Sea region of Abkhazia as parts of Georgia.

Moscow has used diplomatic recognition as an instrument to maintain an armed presence in breakaway regions of the former Soviet Union that it sees as part of its sphere of influence.

In Ukraine, Russia's long-standing support for armed separatists in the eastern regions of Donetsk and Luhansk gave it a platform to invade. Moscow calls its military action in Ukraine a "special operation" and the West decries it as an unprovoked war.

Earlier this month, the International Monetary Fund outlined a three-year $289 million plan to support Georgia's economic reform programme as it grapples with the impact of the war in Ukraine.

Georgia's economy had been recovering well from the COVID-19 pandemic before the war, with economic growth topping 10% last year. Now, however, the IMF estimates that the impact of the war will cut growth to 3% in 2022, fuel inflation and widen Georgia's current account deficit. (Reporting by Marc Jones; editing by Karin Strohecker and Gareth Jones)