Bulgaria on Tuesday rejected reports that the truck linked to the powerful blast that damaged Russia's bridge to annexed Crimea had travelled via its territory.
Alexander Bastrykin, the head of Russia's Investigative Committee, said that the vehicle had passed through Bulgaria, Georgia, Armenia, South Ossetia and Russia's Krasnodar region before arriving on the bridge.
"It has been indisputably established that the truck blown up on the Crimea bridge was never in the territory of Bulgaria," the government said in a statement.
"The Bulgarian government will in no way allow the name of the country to be associated with any involvement in terrorist activity," it said.
Russia has escalated its attacks on Ukraine after the explosion. On Sunday, Russian President Vladimir Putin accused Ukraine of orchestrating the blast describing it as an "act of terrorism".
Mass bombardments of Ukrainian cities by Russia constitute war crimes under international law, the presidents of the Bucharest Nine group of countries, including Bulgaria, said on Tuesday.