By OLESYA VARTANYAN and ELLEN BARRY

TBILISI, Georgia — Georgia said Tuesday that it had foiled a Russian-backed plot against the government as tensions rose a day before the scheduled start of NATO military exercises.

Georgian forces surrounded a tank unit that it accused of being involved in the plot and President Mikheil Saakashvili entered the base to negotiate the unit’s surrender. In a televised address, Mr. Saakashvili said the plot was an attempt by Russia to derail the planned exercises, which he called a “symbolic event.”

“We have information that the Russian Federation wants to exacerbate the situation in Georgia,” Mr. Saakashvili said. “We are asking our northern neighbor to refrain from any provocations.”

Russian officials denied any role in the unrest. Alexei Pavlov, a spokesman for President Dmitri A. Medvedev, called the accusations “too stupid for us to comment on.”

“We don’t consider it necessary to respond to these accusations,” he said. “Georgia is constantly accusing us of something. It doesn’t matter what. All of the internal problems in Georgia are blamed on Russia.”

Details of the alleged plot were murky Tuesday afternoon. Georgia released a series of videos in which Gia Ghvaladze, a former major in the Georgian special forces, was shown trying to recruit assistance in overthrowing Mr. Saakashvili’s government on behalf of Russia. Mr. Ghvaladze was arrested Monday night on charges of organizing a military mutiny, according to police.

According to the video, a commander at the Mukhrovani tank battalion, Col. Koba Otanadze, had offered to supply tanks and heavy armor. A statement from the Interior Ministry said Mr. Otanadze had organized a previous mutiny at the same base eight years ago.

The incident came at a delicate time in relations between Russia and NATO. Wednesday is the official opening of the military exercises, which are scheduled to continue through June. NATO has characterized the exercises as routine, involving fewer than 1,000 soldiers, but Moscow has vigorously protested them.

Last week, Russian border guards took up long-term positions at the boundaries of South Ossetia and Abkhazia, the two breakaway territories that were at the center of a war between Georgia and Russia in August.

NATO and Russia are also at odds over accusations of spying. NATO announced last Thursday plans to expel two Russian diplomats from its headquarters in Brussels over espionage charges, which Dmitri O. Rogozin, Russia’s envoy to NATO, called “a clear-cut provocation.”

Russian media reported Tuesday that Foreign Minister Sergey V. Lavrov had canceled plans to attend a meeting of the NATO-Russia Council this month in protest over the expulsions.

The NATO-Russia Council is the forum where the two discuss cooperation and air their differences, but talks at its highest level were frozen last year over Russia’s war with alliance-hopeful Georgia.

Olesya Vartanyan reported from Tbilisi, Georgia, and Ellen Barry from Moscow.

URL: http://www.nytimes.com/2009/05/06/world/europe/06georgia.html?ref=world