KIEV, Oct, 1 - Ukraine's state energy company, Naftogaz, has failed to pay a maturing $1.6 billion debt, raising risks of a default on the country's sovereign Eurobonds and sending debt insurance costs to seven-month highs, Reuters reported.

The government assured investors on Wednesday they would soon be paid on the bonds, which were due on Sept 30 and have now entered an initial 10-day grace period.