The Ukrainian company's claims against the Russian state over the Crimea assets were left out of a settlement deal with Russia's Gazprom agreed at the end of December, which canceled out all existing arbitration claims by both parties as part of a new transit contract.

Gazprom and Naftogaz entered into an agreement to arrange for the transmission of gas across Ukrainian territory. Naftogaz is thus acting as the transit organizer and assuming the associated risks.

Last week, Russia and Ukraine announced the terms of a new gas transit deal under which Moscow will supply Europe for at least five years via its former Soviet neighbor and pay a $2.9 billion settlement to Kiev to end a legal dispute.

Last week, President Vladimir Putin said Russia wanted to resume direct gas sales to Ukraine -- and would be prepared to reduce the price Kyiv paid by 20%-25%.

In a statement, Gazprom said it had sent a letter to Naftogaz -- signed by Gazprom CEO Alexei Miller -- to "extend the existing contract or to conclude a new gas transit agreement through Ukraine for a period of one year."

Putin said Ukraine still had work to do to align its gas regulatory landscape with that of Europe, questioning whether Kiev would be able to achieve this in time. "That is not up to us," he said. "Therefore, the risk of termination of transit exists."

Alexey Miller pointed out that a number of strategic issues need to be resolved prior to the signing of a new transit contract.

Gazprom has offered to Naftogaz the chance to start over with a clean slate provided all legal disputes were dropped. "There are known cases in international practice when disputes between companies were settled out of court, and we are offering a zero option whereby all court proceedings would cease, all lawsuits would be withdrawn, and we would draw a line under this whole affair," Miller said last month.

The current 10-year agreement between Gazprom and Naftogaz expires at the end of 2019, and the European Commission is brokering talks aimed at putting in place a new contract to take effect from the start of 2020.

PLATTS - "Today we submitted a petition to the Court of Appeal in Sweden," Vitrenko said as the Ukrainian company looks to find legal grounds to continue its efforts to seize Gazprom assets in the Netherlands, Switzerland and the UK to enforce the arbitration award.