Russia will demand that Ukraine prepay for June naturalgas imports, and the first bill will be delivered to Kiev on May 16, Russian EnergyMinister Alexander Novak said Thursday , according to the Wall Street Journal. Novak said the deadline that Ukraine had to settle its gas bill for earlier deliveriesexpired Wednesday and, according to the contract between Russian gas monopolyGazprom and its Ukraine counterpart Naftogaz, Ukraine will have to pay for futuredeliveries in advance.The minister said starting in June Ukraine will receive only the volume of gas it hadpaid for by the end of May.Ukraine has run up a bill for Russian gas, which Gazprom said has reached $3.5billion. Naftogaz confirmed earlier Thursday that no payment has been made tocover the debt.