Russian gas giant Gazprom has threatened to cut off gas deliveries to Ukraine if Kiev does not pay up front for March deliveries in the next two days, chief executive Alexei Miller said on Tuesday.
Gazprom said that Ukraine had 219 million cubic metres of gas let that would be used up in two days. If Kiev did not pay for the next batch of supplies, then the state-owned company would cut off supplies.
"It creates serious risks for the transit to Europe," Miller said in a statement.
Ukraine's state-run gas company Naftogaz said on Monday that Gazprom had failed to fulfil its obligations by delivering less than half of the gas that it had paid for up front.
The Ukrainian complaint came just days after Moscow said it was sending some gas paid for by Kiev directly to rebel-held regions in the country's east.
Moscow has previously cut of gas deliveries to Ukraine, most recently in the middle of 2014. Ostensibly relating to a dispute over the price Ukraine paid for its gas, the stoppage came as Kiev fought a conflict with pro-Russian separatists in eastern Ukraine. Supplies were resumed in December last year, after a deal was brokered by the European Union.
Gazprom's latest threat comes as the Ukraine conflict continues to rumble on, despite Kiev and Moscow reaching a ceasefire last week. With the United States and the European Union openly debating the next round of sanctions to be imposed on Russia, Moscow has reignited the gas war once again.
The EU relies on Russia for around a third of its gas needs, half of which is delivered via Ukraine's pipelines.
European countries were not affected by last year's dispute but previous gas wars have ended with some states running low on natural gas supplies.
Ukraine has long sought to reduce its dependence on Russia for its energy needs and hopes to increase its supplies from Europe, as well as boost its own domestic exploration efforts, although these remain long-term goals.
Ukraine could potentially seek to import gas from some EU countries via reverse flows, if Moscow does halt supplies.