In December, Russia agreed to reduce gas prices for Kiev by about a third, to $268.50 per 1,000 cubic metres from around $400 which Ukraine had paid since 2009, after ousted President Viktor Yanukovich spurned an EU trade deal in favour of closer ties to Moscow.
Kupriyanov said Ukraine's outstanding gas debt stood at $1.55 billion for 2013 and gas deliveries so far this year, Reuters reported.
"It seems that with such gas payments and fulfilment of its obligations Ukraine may not keep its current gas discount. The gas discount agreement assumed full and timely payment," he said.
The deal allowed for the price to be revised quarterly between the 5th and 10th day of the first month every quarter.