Ukraine’s state-owned energy firm Naftogaz will go to court to try to seize Gazprom’s assets in Europe after the Russian energy firm failed to make a payment ordered by an international tribunal, Naftogaz’s deputy chief said on Monday.

Kiev and Moscow were drawn into a new gas dispute on March 1, after Russia’s state-owned Gazprom unexpectedly decided not to restart supplies to Ukraine, forcing Kiev to reduce supplies despite freezing temperatures and leading to the closing of many schools and universities.Gazprom said it had returned a prepayment to Ukraine and would not restart gas supplies because an additional agreement to the existing arrangements had yet to be reached.

Gazprom’s move follows a decision on February 28 by the Stockholm arbitration court stating that Gazprom had to pay $2.56 billion to Naftogaz after weighing mutual claims and counterclaims related to gas supplies and transit after several years of commercial disputes.

“For us it’s clear that they won’t do that (pay) so we will start arresting their gas and other assets of Gazprom in Europe, not in Ukraine. We will go to courts in Europe,” Natogaz’s chief commercial officer Yuri Vitrenko told Reuters in Brussels.

However, Naftogaz will not seek to seize Russian gas transiting through Ukraine to European clients, he added, saying: “We don’t want to create any kind of political ambiguity here in the EU that Ukraine is not a reliable transit country.”

Gazprom is appealing against the Stockholm ruling and is seeking to cancel a 2009 gas transit contract with Ukraine, escalating a dispute which the European Union says could threaten gas flows.

Naftogaz said it expected talks with Gazprom later this week to be the last before it files fresh complaints with the Stockholm arbitration tribunal. Among other issues, it wants compensation for Gazprom’s refusal to supply gas this winter.

The EU and Western clients had hoped the Stockholm arbitration would resolve one of the many thorny disputes between Kiev and Moscow. Instead, the two sides are raising the stakes amid tricky discussions over future gas transits through Ukraine when the current contract expires at the end of 2019.