The United Nations observer mission in Georgia on Monday concluded that the plane that shot down an unmanned Georgian reconnaissance aircraft last month belonged to the Russian military.
Russia denied the claim and the report is likely to aggravate already fraught relations between the two countries. Tensions have been high for months over Russia's support for the Georgian separatist province of Abkhazia - where the aircraft was shot down - and Georgia's drive to join NATO.
The observers' report said both sides had violated an Abkhazia cease-fire agreement - Russia by shooting down the drone and Georgia by flying it over Abkhazia.
The reconnaissance drone was shot down over the separatist province on April 20. A video taken by the pilotless aircraft shows a fighter jet firing a missile in its direction.
Abkhazia's separatist government claimed the drone was shot down by one of its L-39 jets. However, the plane in the video had a distinctive twin-finned tail, and the report concluded it was either a Russian-made MiG-29 or Su-27 - neither of which Abkhazia possesses.
The report of the U.N. Observer Mission in Georgia said radar tracking shows that after the missile was fired, the plane headed into Russian airspace.
"Absent compelling evidence, this leads to the conclusion that the aircraft belonged to the Russian air force," the report said.
But Russian Defense Ministry spokesman Col. Alexander Drobyshevsky said "there cannot be any talk of any kind of violation of the state border of Georgia or of the shooting down of an unpiloted flying apparatus," according to the RIA-Novosti news agency.
Georgian President Mikhail Saakashvili said Monday that "Georgia for the first time has confirmation from the U.N. that Russia has committed an act of aggression against Georgia," the Interfax news agency reported.
"All of this demands a tough reaction by the international community," he was quoted as saying.
Georgia has long accused Russia of aiming to annex Abkhazia and another separatist region, South Ossetia. Both have been outside the Georgian government's control since the end of fighting in the mid-1990s.
Russia does not formally recognize either regions' separatist governments, but it maintains close contacts with them and has granted passports to most of the regions' residents. Russia also has peacekeeping forces in both regions; Georgia accuses the forces of supporting the separatists.
Last month, Russia called for upgrading ties with Abkhazia, a move that outraged Georgia. Russia, meanwhile, accuses Georgia of marshaling forces on the outskirts of Abkhazia with the aim of reasserting control by force.
In response to that, Russia increased its peacekeeping force in Abkhazia, saying it needs to protect Russian citizens.
Abkhazia claims to have shot down seven Georgian drones this year. Georgia has denied all the claims except for the April 20 incident, which it also initially denied.
However, the observer report said wreckage from at least two other incidents was confirmed to be that of Hermes 450 drones such as those used by Georgia.