(Recasts, adds quotes, previous MOSCOW)
By Margarita Antidze
TBILISI, May 26 (Reuters) - The United Nations said on Monday that a Russian air force plane shot down an unmanned Georgian spy drone over Abkhazia last month, strengthening Tbilisi’s claims that Moscow is aiding the rebel territory.
A U.N. report compiled from video footage, witness statements and radar records was the weightiest independent endorsement to date of Tbilisi’s allegation -- denied by Moscow -- that a Russian jet downed its spy plane on April 20.
The report said radar records showed the fighter jet headed into Russian airspace after shooting down the spy plane over breakaway Abkhazia.
"Absent compelling evidence to the contrary, this leads to the conclusion that the aircraft belonged to the Russian air force," said the report posted on the Web site of the UN mission in Georgia, www.unomig.org.
Russia’s air force could not immediately be reached for comment. Russia has previously denied any involvement in downing the spy plane, saying it was shot down by anti-aircraft batteries operated by Abkhazian separatists.
Georgian President Mikheil Saakashvili told reporters that the UN report was "the first ever case when an international organisation ... pointed at Russia for such actions."
The report contained "a direct accusation against Russia of an act of aggression," he said
Last month’s incident escalated tensions between Moscow and Tbilisi, which were already locked in a bitter dispute over Russian support for Abkhazia and Georgia’s ambitions of joining NATO.
Georgian officials had released a video, recorded by the spy plane’s onboard camera before it was shot down, which showed a fighter plane approaching it and then launching a missile in its direction.
Abkhazia is recognised internationally as part of Georgia. But it has run its own affairs since it drove out Georgian forces in a separatist war in the 1990s.
The conflict could frustrate Tbilisi’s ambitions of joining NATO, and is a source of volatility in a region that is part of a vital transit route for oil and gas exports from the Caspian Sea to world markets.
Russia provides assistance to the separatists and has peacekeepers in Abkhazia, prompting Tbilsi to accuse Russia of a creeping annexation of the region.
The UN report criticised Georgia over the spy plane incident, saying flying surveillance aircraft over Abkhazia was in violation of a 1994 ceasefire deal called the Moscow Agreement.
"It stands to reason that this kind of military intelligence-gathering is bound to be interpreted by the Abkhaz side as a precursor to a military operation, particularly in a period of tense relations between the sides," the report said.
But it said that was no justification for Russia shootingwn a Georgian plane.
"Enforcement action by third parties - in this case the Russian Federation -- in the zone of conflict is fundamentally inconsistent with the Moscow agreement and ... undercuts the ceasefire and separation of forces regime," it said. (Writing by Christian Lowe; Editing by Richard Balmforth