Russian state controlled oil firm OAO Gazprom could unblock its gas shipments to Europe Friday on the condition that a monitoring mission led by the EU tracks the gas flow through Ukrainian pipelines.

Gazprom is expecting to sign an agreement, the company’s CEO Alexei Miller said, according to the Associated Press.

European Union monitors have already arrived in Ukraine’s capital city of Kiev.

Gazprom halted all supplies to European countries through Ukraine Wednesday. The company said it stopped shipments after realizing Ukraine wasn't shipping some fuel intended for European customers, an allegation denied by Naftogaz.

Gazprom provides about a quarter of gas consumed in Europe.