Russia says the armed seizure of a Ukrainian oil refinery in which it has a stake is a "flagrant outrage".
Russian First Deputy PM Sergei Ivanov accused Kiev of "inaction" after a former head of the Kremenchuk refinery, backed by armed guards, was reinstated.
Pavel Ovcharenko cited a court order returning him control of the refinery.
Kremenchuk's Russian oil supplier - and shareholder - has suspended deliveries, prompting fears of a fresh row between Moscow and Kiev over energy supplies. undefined
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The Russian firm Tatneft, based in the Tatarstan region, has a 28.8% stake in the refinery.
The Tatarstan government has urged Ukraine's chief prosecutor to launch criminal proceedings against those who seized the plant.
Russia and Ukraine only recently ended months of dispute by negotiating a deal over the supply of natural gas.
Russian giant Gazprom had been threatening to suspend gas deliveries to Ukraine over alleged unpaid bills.
Ukraine had in turn accused Russia of using energy as a political lever against its pro-Western government.
'Heading for crisis'
Mr Ivanov said on Friday that the
He urged Kiev to intervene, saying the "Ukrainian authorities' inaction is bewildering".
Armed men entered the Kremenchuk complex on 19 October.
The refinery's boss, Sergei Glushko, was forced from office and its former chief, Pavel Ovcharenko, was reinstated.
The change prompted Tatneft to suspend oil supplies.
On its website, Tatneft says the members of a private security firm had forcibly entered the refinery, "battered" its guards and briefly corralled board members into a room.
Mr Ovcharenko told AFP news agency the raid had been conducted by bailiffs and had the backing of a court order.
Mr Glushko, quoted by Reuters news agency, said Kremenchuk would stop functioning if it turned to domestic oil supplies and imports from other sources to replace the Russian oil.
"Without Russian oil we cannot do anything," he said. "Give it a week more and we will be in crisis."
dispute over Kremenchuk had "harmed greatly the relations between Ukrainian and Russian investors".