The Ukrainian opposition said the country's gas pipelines can be modernized only in a trilateral format of Ukraine, Russia and the EU.

"We've signed a memorandum with our European partners to modernize the gas transportation system (GTS), and the issue of operating the GTS, of modernizing and developing it can be decided only in a trilateral format," Leader of the Batkivschyna faction Arseniy Yatseniuk said at a briefing.

This cannot be done in a bilateral format, he said. "That would mean ownership of the Ukrainian GTS passing to Russia," he said.