MOSCOW, June 12 - Russian natural gas exporter Gazprom will halt supplies to Ukraine if it fails to pay off part of its gas debts by Monday, chief executive Alexei Miller said on Thursday, raising fears of disruptions in gas flows to Europe, Reuters reported.

Miller said that if Ukraine failed to pay $1.95 billion to Gazprom it would start requiring Kiev to pay in advance for further shipments, and that if it did not receive any money at all, it would cut off supplies.