Russia on Wednesday geared up to sign a wide-ranging alliance with Georgia's breakaway region of South Ossetia that will further cement its control over the territory despite fierce condemnation from the West.

President Vladimir Putin is set to ink a deal in Moscow with South Ossetian leader Leonid Tibilov that officially makes Russia responsible for defending the self-declared republic, where the Kremlin has stationed thousands of troops since a war with Georgia there in 2008.

The signing of the controversial pact comes as Russia marked one year to the day since Putin signed off on the annexation of Ukraine's Black Sea republic of Crimea in a seismic shift slammed by Kiev and the West as an illegal land grab.

Officials in pro-Western Georgia have blasted the pact —similar to one sealed between Moscow and a second separatist enclave Abkhazia last year — as a "de facto annexation" of its territory.

European Union foreign policy chief Federica Mogherini warned that the treaty would further destabilise the volatile region.

"The signature by the Russian Federation of a so-called 'Treaty on Alliance and Integration' with Georgia's breakaway region of South Ossetia... will be yet another step that goes against ongoing efforts to strengthen security and stability in the region," she said in a statement.

Abkhazia and South Ossetia broke away from Georgia after civil wars in the 1990s that followed the break-up of the Soviet Union.

Moscow officially recognized their independence after fighting a five-day war with Georgia in 2008.

Only a handful of other countries recognize the regions' independence.