Lithuanian prosecutors state that Russia's military intelligence service, the GRU, was responsible for an arson attack on an Ikea furniture store in the Baltic state's capital, Vilnius, last year.
Two Ukrainian suspects have been arrested – one in Lithuania, the other in Poland – over the attack, which prosecutor Arturas Urbelis called "an act of terrorism".
He said an investigation of intermediaries had established that "this is connected with military intelligence, with the security services."
Poland's Prime Minister Donald Tusk said Lithuania had "confirmed our suspicions that responsible for setting fires to shopping centres in Vilnius and Warsaw are the Russian secret services."
"Good to know before negotiations. Such is the nature of this state," he wrote in a post on X.
Russia has denied repeated allegations by Nato countries that its secret services are engaged in sabotage operations across Europe.
Security experts see it as a systematic campaign of "hybrid warfare" to undermine European support for Ukraine's defence against the Russian invasion that began in February 2022.
The arson attack in Vilnius last May did not cause casualties, but that month a similar attack destroyed a huge shopping mall in the Polish capital Warsaw.
Prosecutor Urbelis said the two suspects - both teenagers - had held a secret meeting in Warsaw and agreed to set fire to shops in Lithuania and Latvia for a reward of €10,000 ($11,000; £8,400) and a BMW.
