Despite cease-fire declarations, pro-Ukrainian and pro-Russian militias are still reportedly clashing at several locations in south-eastern Ukraine.

Among those going into battle from the Ukrainian side are some 500 trained fighters in the self-declared Azov battalion, backed by Jewish energy magnate and Dnipropetrovsk region governor, Igor Kolomoisky, according to Israel’s Ma’ariv daily.

A Ukrainian military spokesman said pro-Russian separatists on Tuesday opened fire at Ukrainian army positions in the Donbass region and vandals blew up railway tracks in Logansk in order to impede rail traffic in the area.

A source at Ukraine’s National Security and Defense Council, cited by Voice of Russia, claimed that “Kolomoisky is the most outspoken opponent of the plan on settling the situation in the East of Ukraine.”

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In April, Kolomoisky placed a $10,000 bounty on the head of any Russian “saboteur,” caught, according to the UK’s The Guardian, which added that turning over a grenade launcher to Kiev authorities would net finders $2,000, and $1,500 for every heavy machine gun handed in.

Meanwhile, on June 21, Russia’s Investigative Committee (IC) ruled to indict Kolomoisky and parliament-appointed Interior Minister Arsen Avakov on war crimes charges, according to Russia’s Itar-Tass News Agency.

“In the near future the investigators will put Avakov and Kolomoisky on the international wanted list and request a court warrant for their arrest,” according to IC spokesman Vladimir Markin

On Monday, American President Barack Obama spoke with Russian counterpart President Vladimir Putin, calling on the latter to support efforts to defuse tensions in the area or face sanctions, the White House said, according to Voice of America.

“Russia will face additional costs if we do not see concrete actions to de-escalate the situation,” White House Spokesman Josh Earnest told reporters.

“The president called upon President Putin to press the separatists to recognize and abide by the ceasefire and to halt the flow of weapons and material across its border into Ukraine,” Earnest said.

“The president emphasized that words must be accompanied by actions and that the United States remains prepared to impose additional sanctions should circumstances warrant, in coordination with our allies and partners,” he said, according to a Reuters report.