Since 2014, Lithuania has jailed several of its citizens for spying for Russia, once the Baltic country's Soviet overlord. In 2017 it handed down a 10-year jail sentence on a Russian it said had tried to set up a spy ring in Lithuania for Moscow's FSB security service.
"All of these people, who executed tasks for an intelligence organisation of the Russian Federation, are connected to political.parties in some way," prosecutor general Evaldas Pasilis said of the arrests this year.
The prosecutor declined to say how many arrests had been made in 2018 but said none of those held was connected to parties represented in parliament. The charges could bring sentences of up to 15 years in prison.
The Russian Embassy in Vilnius could not be reached for direct comment on Wednesday. But it said on its website: "There is no doubt: this new espionage fuss is one more serious anti-Russian action by the Lithuanian authorities."
Pasilis said one of the accused was a former vice-mayor of the capital Vilnius, Algirdas Paleckis. He led the small political.party Frontas during the years 2008-2014 and was vocal in protesting against Lithuania's membership of the NATO alliance.
Russian intelligence was interested in "the most sensitive topics for the society", said Pasilis, such as the ongoing trial of former Soviet officers, mostly in absentia, charged with the killings of 14 civilians in January 1991 during an attempted takeover of a Lithuanian government which was seeking independence from the Soviet Union.
From 2014 to 2017, 12 people were accused of spying for Russia or its ally Belarus, Lithuanian authorities say. Five have been sentenced and one case is currently in court. The remaining six are still under investigation.
(With inputs from agencies.)