MOSCOW, Aug. 1 - RosUkrEnergo, the sole supplier of Ukraine's gas imports, urged Naftogaz to pay outstanding $371.8 million debts for gas supplied by Aug. 15 or face a lawsuit, a newswire reported Wednesday.

RosUkrEnergo, the Swiss-registered gas trader, sent a letter to Naftogaz Chairman Oleksandr Bolkisev urging to pay the debt and threatened to take the case to the Stockholm Arbitration Court.