Ukraine's gas dispute with Russia is heating up. Pictured, Russian Energy Minister Alexander Novak arrives in Brussels to meet with his Ukrainian counterpart. Reuters/Eric Vidal

Ukraine’s natural gas and oil firm Naftogaz accused Russia’s Gazprom Monday of failing to uphold an agreement signed last year to supply Ukraine with gas over the winter months ahead of a planned meeting between the countries’ energy ministers in Brussels to work out a compromise over deliveries. Last week, Gazprom threatened to cut off supplies if Ukraine didn’t pay for them in advance, but Ukraine made a last minute payment to keep gas flowing through the middle of this week.

“In February, the agreement was violated by the Russian side. Gas for which we had paid in advance was not delivered in full last month,” said Naftogaz chief executive Andriy Kobolev, according to Reuters. “The deal is continuing to be violated this month. This violating needs to be balanced by an increase in gas deliveries to Ukraine from the EU.”

A gas cutoff is still possible and would devastate an already ailing Ukrainian economy. Russia has continually leveraged their gas monopoly over Ukraine as a way to pressure Kiev over its war with pro-Russian separatists in the east of the country. Last week, a Russian presidential aide said Gazprom was prepared to work directly with rebel leaders to keep gas flowing to eastern Ukraine while still cutting off the rest of the country, which is controlled by a pro-European government. Civilians in battle zones in Donetsk and Luhansk Oblasts have suffered under food shortages, power outages and intense shelling for months.

Diplomats and leaders from Europe and the U.S. are focused on the Ukraine-Russia dispute in various meetings around the region this week. The leaders of Ukraine and Russia are scheduled to speak with their German and French counterparts over the phone Monday night to discuss gas deliveries and a peace agreement they made in Minsk, Belarus last month.

U.S. Secretary of State John Kerry said he told his Russian counterpart, Sergey Lavrov, in Geneva Monday that if allegedly Russian-backed rebels in Ukraine did not respect a ceasefire, “there would be inevitable further consequences that would place further strain on Russia’s already troubled economy,” according to Reuters. The U.S., Ukraine and their European allies accuse Russia of directly intervening on behalf of separatists in the east.