By Kazbek Basayev

TSKHINVALI, Georgia (Reuters) - A pro-Russian former KGB officer has won the presidency in Georgia's breakaway region of South Ossetia and suggested he would push for the tiny territory to join Russia.

A mountainous region of about 30,000 people, South Ossetia has been at the heart of Georgia's bitter relations with Russia since breaking from Georgian control in a war in the 1990s.

Moscow recognized it as an independent nation after a brief war with Georgia in 2008. Internationally it is only recognized by Venezuela, Nicaragua and the Pacific nation of Nauru.

The victory of a Kremlin-backed candidate is certain to bolster Moscow's influence in the region as it seeks to complicate aspirations by U.S.-backed Georgia to join NATO.

According to results released on Monday, Leonid Tibilov won more than 54 percent of the vote in Sunday's presidential runoff against regional human rights ombudsman David Sanakoyev.

Georgia's government dismissed the election as illegitimate, calling South Ossetia "occupied" territory and saying it would urge the international community to join its criticism.

"Our position will be tough as ever and Tbilisi will address the international community for reaction," Georgian Deputy Foreign Minister Nino Kalandadze said.

Russia has a military base in South Ossetia and has spent about $1 billion supporting the impoverished region since the 2008 conflict.

"We will develop the relationship with Russia in all areas. We are aiming to make an old dream about the reunification of South and North Ossetia a reality," Tibilov, 60, told reporters on Sunday in the region's capital, Tskhinvali.

North Ossetia is part of Russia and Tibilov's call implies a de facto unification of the region with Russia.

Analysts however say Moscow is unlikely to push for unification soon in order to avoid antagonizing Western powers, which reject South Ossetia's independence claim and would be deeply alarmed by a Russia's physical expansion.

(Reporting by Kazbek Basayev; Additional reporting by Margarita Antidze in Tbilisi; Writing by Thomas Grove Editing by Maria Golovnina)