KIEV, April 14 ??“ Naftogaz Ukrayiny, the national oil and gas company, has been running an undisclosed debt to RosUkrEnergo, a Gazprom-controlled gas trader, for gas supplies so far this year, a company spokesman said Friday.

The debt started to mount shortly after Russia had forced Ukraine to accept a 90% gas price hike stating Jan. 1, while the government had not yet allowed domestic prices to increase.