MOSCOW Russia's Gazprom GAZP.MM said on Monday Ukraine had failed to pay at least part of its gas debts by a 0600 GMT deadline and would now have to pay up front for deliveries.
It said in a statement that Ukraine's state-controlled Naftogaz had also failed to pay for June deliveries, suggesting supplies could now be cut.
"Today, from 10:00 a.m. Moscow time, Gazprom, according to the existing contract, moved Naftogaz to prepayment for gas supplies ... Starting today, the Ukrainian company will only get the Russian gas it has paid for," it said.
(Reporting by Vladimir Soldatkin, writing by Elizabeth Piper, editing by Kevin Liffey)