Officials from the European Union, Russia, and Ukraine are meeting in Berlin to try to resolve a natural-gas dispute between Moscow and Kyiv.
Russian state-owned gas giant Gazprom says Ukraine's gas debt will amount to some $5.2 billion by June 7, and has set a June 2 deadline for Kyiv to pay that debt.
On May 28, Russian Energy Minister Aleksandr Novak insisted Ukraine must pay at least $2 billion by May 30 or face gas cuts beginning on June 3.
EU Energy Commissioner Guenther Oettinger said ahead of the talks that Ukraine must pay a down payment and in return Moscow must offer a fair price for further deliveries.
Oettinger said the price of $485 per 1,000 cubic meters of gas that Russia is demanding was "unacceptable."
Ukraine wants a price of $268.50 per 1,000 cubic meters.
The EU is worried a suspension of Russian gas shipments to Ukraine would leave some EU countries either with reduced supplies or totally cut off from Russian deliveries that pass through pipelines in Ukraine.
Ukraine's crisis will also be the main item on the agenda for lawmakers from 28 NATO member countries who are gathering in Vilnius on May 30 for the spring session of the NATO Parliamentary Assembly.
The gathering comes amid heightened concerns in the Baltic states and Eastern Europe about Russia's role in Ukraine's crisis.
The assembly -- which also includes delegates from NATO partner countries, the European parliament, and various international organizations -- is expected to adopt a resolution on Ukraine.
Regarding NATO's future eastward enlargement, the NATO Parliamentary Assembly is expected to create a new document stressing the need for the alliance to leave the door open for future expansion.
Andriy Parubiy, the secretary of Ukraine's National Security and Defense Council, is expected at the May 30 plenary session along with NATO Secretary-General Anders Fogh Rasmussen.
With reporting by Reuters, AFP, and ITAR-TASS