The head of Russia’s state-run energy company Gazprom said Friday that Ukraine has stopped paying for Russian gas supplies, which could trigger a repetition of 2009’s so-called “gas war” between the two countries, according to RIA Novosti.

Alexei Miller said crisis-hit Ukraine owes Russia about $1.89 billion in unpaid natural gas bills after failing to pay for February supplies.

“This violates our contract and international trade practices. We cannot supply natural gas for free,” Miller told reporters in Moscow.

“Ukraine must pay off its debts and current deliveries or face the risk of returning to the 2009 scenario, when Russia halted all deliveries to Europe via Ukraine’s pipeline system for two weeks,” he said.

Gazprom has already announced that it will annul its discount on natural gas sales to Ukraine from April, following last month’s ouster of Ukrainian President Viktor Yanukovych.

Russia and Ukraine have long fought over natural gas deliveries, jeopardizing supplies to Europe, a major Russian gas buyer. In 2009, the most severely affected countries were in southeastern Europe as Bulgaria was forced to stop production at some of its industrial plants, while Slovakia even declared a state of emergency.