"This is evidently a crude fabrication, utter nonsense, which seems to be designed to raise the temperature of the anti-Russian campaign in Georgia," the ministry said in response to a report on a Georgian TV channel, Rustavi 2, that investigators had found a "Russian trace" in their enquiries.
"Some people in Tbilisi seem to be unhappy that after an agreement was reached on the terms of and procedure for the closure of Russian military bases, this [anti-Russian] campaign started to fade," the ministry said.
The Foreign Ministry said the command of the group of Russian troops in the region had "categorically rejected insinuations" that some of its servicemen had been involved in the Tbilisi incident or had been arrested when trying to leave Georgia.
"We can only regret that no Georgian officials have refuted this fabrication, which has been invented and blown out of proportion by a pro-governmental television channel," the ministry said.
Gela Bezhuashvili, the secretary of Georgia's national Security Council, had previously said that the grenade discovered on May 10 during George Bush's speech on the capital's Freedom Square was of an "engineer" type and could not be easily turned into an offensive weapon.
However, the FBI said the grenade was live and only a weak percussion lock prevented the detonator from working.