(Adds Russian reaction, details)

By Niko Mchedlishvili

TBILISI, Aug 24 (Reuters) - Georgian forces fired at a plane they believed was Russian after it violated the Caucasus republic's airspace on Wednesday, a senior interior ministry official said.

The incident marks an intensification of a row between the two countries in which Georgia has accused Russian planes of violating its border and of dropping a missile near Tbilisi.

Russia called the Georgian statement a provocation. It has not reported any plane missing, and when asked specifically about the Georgian statement an official denied Russian aircraft had violated Georgian airspace.

"The day before yesterday at 22:24 in the mountains of Upper Abkhazia we opened fire on a Russian plane, after which we heard an explosion," Shota Utiashvili, head of the interior ministry's analytical department, told Reuters on Friday.

It was not clear what caused that explosion.

"The forest is on fire there, but we cannot confirm that the plane was shot down," Utiashvili said, adding that the interior ministry would send a helicopter to the area on Saturday to investigate.

Utiashvili could not say what kind of airplane it was, but insisted it was Russian. He said that it had headed towards a deserted mountain part of the rebel Georgian region of Abkhazia that was held by separatists.

Upper Abkhazia, where Georgia says the shooting incident took place, is a small mountainous part of the breakaway Abkhazia province still controlled by Tbilisi.

Moscow-backed Abkhazia is a regular source of tension between the two countries, as Georgia seeks to regain control over the region.

INTERNATIONAL REPERCUSSIONS

Moscow says its planes have never violated Georgia's border.

"This is another provocation in the information campaign waged against us," Interfax news agency quoted Alexander Drobyshevsky, an aide to Russian airforce commander, as saying.

"I say this officially, Russian airplanes did not violate the Georgian air space."

Interfax also quoted an official from Abkhazia's defence ministry as saying: "We haven't registered recently any downings of any plane at territory controlled by the Abkhaz side."

Georgia said on Wednesday two Russian planes had violated its border around the same area. Two weeks ago it accused Russian jets of dropping a missile near the capital, Tbilisi.

Russian news agencies quoted Abkhaz authorities as saying earlier on Friday their forces had fired warning shots on Thursday at an unidentified plane that crossed into Abkhazia from Georgia.

The row over aircraft has highlighted a crisis in relations between Russia and Georgia, which has been deepening since U.S.-educated President Mikhail Saakashvili began moving his republic of five million people out of Moscow's orbit.

Russia last year severed air, sea and postal links with its southern neighbour over a spying row. Before that, Moscow had banned imports of Georgian wine and mineral water, both major sources of revenue, citing health concerns.

The missile incident has had repercussions beyond the region, turning into an irritant in ties between Russia and the United States. (Reporting by Niko Mchedlishvili, writing by Oleg Shchedrov, editing by Toby Reynolds; oleg.shchedrov@reuters.com, oleg.shchedrov.reuters.com@reuters.net; +7 495 775 1242))

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