MOSCOW, May 3 (Reuters) - The European Union should share responsibility for replenishing natural gas storage sites in Ukraine to avoid threats to European gas supplies, Russia's Energy Minister Alexander Novak said on Saturday, Russian agencies reported.
"We think that the present situation has become critical and urgent measures need to be taken to resolve it," Novak said, in comments cited by Interfax.
Novak said Ukraine's storage sites will need to store at least 18.5 billion cubic metres of gas in the coming winter. At present the sites contain between 4 and 6 billion, he said.
"This means that ... in the summer period from May until September ... there must be secured the injection of gas in underground storage sites in the western part of Ukraine in volumes of around 12 billion cubic metres," Novak added, in comments also reported by other agencies including RIA novosti.
A third of the EU's gas import needs are met by Russia, with almost half of that passing through Ukraine, which is in a pricing dispute with Russian gas exporter Gazprom, its third in the past decade.
Relations between Russia and the West have fallen to their lowest ebb since the Cold War following Moscow's annexation of Ukraine's Crimea region and the outbreak of clashes involving pro-Russia militia in the east of the country.
Gazprom says Kiev owes it some $3.5 billion for gas already delivered.
Novak on Friday said if Russia does not receive pre-payment for June deliveries by May 31, it is possible Gazprom will reduce gas supplies to Ukraine.
(Reporting by Jason Bush; Editing by Megan Davies and David Holmes)