Ukrainian prosecutors said they had broadened a criminal investigation into pro-Russian lawmaker Viktor Medvedchuk, accusing him of colluding to finance separatist forces in the eastern Donbas region.
The October 8 announcement increases pressure on Medvedchuk, whom prosecutors initially targeted in May with allegations of treason.
That has added to tensions between Moscow and Kyiv.
At a joint briefing in Kyiv, Prosecutor-General Iryna Venediktova accused Medvedchuk of conspiring with officials from former President Petro Poroshenko's government to buy coal from mines in separatist-held areas of eastern Ukraine, as a way to finance the separatists.
"We are talking about the sale of state interests and the financing of Russian terrorists," Ivan Bakanov, the head of the state security service, said at the briefing.
"While our soldiers were being killed at the front, the state sent suitcases of cash to the leaders of terrorist organizations," Venediktova said.
Poroshenko's party called the accusations an effort to divert attention from President Volodymyr Zelenskiy government's own wrongdoing.
Zelenskiy defeated Poroshenko in the 2019 election to win the presidency.
Medvedchuk's political party, Opposition Platform-For Life, also dismissed the new accusations and accused Zelenskiy's government of trying to "divert people's attention from their catastrophic failures."
Medvedchuk is a Ukrainian citizen but has close ties with Russian President Vladimir Putin and has said Putin is godfather to his daughter.
His political party is the second largest in parliament.
Ukraine has been at war with Russia-backed separatists in eastern Ukraine since 2014.