EU diplomatic chief Federica Mogherini called on Russia’s natural gas giant Gazprom to fulfill its contractual obligations and resume shipments to Ukraine.

The latest gas dispute between the two warring neighbors began after an arbitration court ordered Gazprom to pay Ukraine $2.56 billion as part of an earlier settlement, according to AFP.

Gazprom vowed to challenge the decision in court and refused to resume supplies to Ukraine for the first time in more than two years on March 1.

The decision coincided with a bitter cold spell across much of Europe. Ukraine was forced to ask schools to close and factories to cut production while it purchased additional volumes from its western neighbors.

EU diplomatic chief Federica Mogherini said she discussed the standoff during a visit to Kiev with Ukrainian President Petro Poroshenko.

“We agree that Gazprom must respect its contractual obligations,” she told reporters.

Mogherini added during a later meeting with students that EU Energy Commissioner Maros Serfcovic was already conducting “highly intense consultations” about the conflict.

She said the EU was “ready” to help mediate but provided no details about the nature of the talks held so far.

The $2.56 billion awarded to Ukraine’s state energy company Naftogaz stems from a court case in which Gazprom and Naftogaz are each suing each other for tens of billions of dollars.

The arguments are over an expensive 10-year contract Ukraine signed in 2009 after Gazprom cut its deliveries in the middle of the winter.

The deal runs out at the end of next year and there is no guarantee that Ukraine will sign a new one because it now imports much greater volumes from central Europe.

Roughly 15 percent of the gas Europe buys from Russia is transported through Ukraine.