Ukrainian authorities have launched a criminal case against an unnamed Russian bank for allegedly funnelling $3.75m into militant groups' bank accounts.
Ukraine's state security service (SBU) said that the bank was "providing financing for terrorists" in March and April.
The SBU alleged that the bank transferred around $200 (£120, €145) and $500 per day to individuals who were later involved in the takeover of offices in the eastern Ukraine city of Luhansk.
Ukraine's acting president Oleksandr Turchynov announced a military operation in the eastern Donetsk region to crack down on pro-Russian protesters who have seized government buildings.
The goal of the "anti-terrorist operation" was to protect Ukraine's citizens and stop criminal activity and attempts to tear the country apart, said Turchynov.
"An anti-terrorist operation began in the north of Donetsk Oblast. It will be conducted step-by-step, responsibly, deliberately. The goal of these actions, I want to underline, is to defend the citizens of Ukraine," Turchynov told the Ukrainian parliament.
"I call on those who want to show their heroism – join the National Guard or the Ukrainian army or police units. But smashing the windows of the Verkhovna Rada is not heroism at all."
He was referring to a group of pro-Russian activists who gathered near the parliament building in Kiev to demand the resignation of interior minister Arsen Avakov.