Ukraine's debt for Russian gas deliveries has reached $3.5 billion as of
the end of April. Russia has decided to switch to a prepayment scheme
due to the outstanding bills, in full accordance with the countries'
contract. Following this decision, Gazprom prepared an advance bill for
Ukraine's Naftogaz for June deliveries. In case of non-payment, Russia
can suspend the gas supply to Ukraine starting June 3.