The debt was incurred as companies working in Ukraine failed to pay Gazprom for natural gas stored in Ukrainian underground tanks, Ukrainian Fuel and Energy Minister Yuri Boiko said in a interview Saturday.

A protocol to be signed Monday transfers $600 million in gas from Ukraine to Gazprom with settlement terms for the rest of the debt yet to be determined, Itar-Tass reported Saturday.

Gazprom Friday told its European partners gas supplies for Ukrainian consumers would be reduced if the Ukrainian government did not reach a settlement agreement in October, Itar-Tass said.