Ukraine's state gas and oil company Naftogaz said on Friday it had no debts to Russian gas giant Gazprom and promised it would ensure uninterrupted transit of Russian gas to European customers, Reuters reports.

"Naftogaz Ukrainy has no debts to Gazprom...Naftogaz will carry out its obligations to Gazprom and RosUkrEenergo by ensuring transit of all volumes in full to European countries," the company said in a statement.

It said any suggestion of a debt of $500 million was a question to be addressed to RosUkrEnergo, a intermediary which oversees supplies of imported gas to Ukraine. Gazprom on Thursday said total debts amounted to $1.5 billion and threatened to cut supplies from Monday unless arrears were paid.