TOKYO • Japan said yesterday it was "truly regrettable" that the United States military had restarted flights of its CH-53 helicopters after one burst into flames last week, saying it wanted further reassurances over safety.

The US resumed operations with the helicopters yesterday, after grounding them for a week following the blaze in an empty field on the western Japanese island of Okinawa.

At the time, the US military said the blaze occurred after the aircraft had landed in the field and no crew were injured.

Japan's Defence Minister Itsunori Onodera told reporters it was "truly regrettable" that the flights had resumed "without enough explanations".

Deputy government spokesman Kotaro Nogami said US officials had briefed their Japanese counterparts, but Tokyo was not satisfied and would "continue asking for further explanations from the US side".

Mr Onodera had previously called for the helicopters to be idled until their safety can be guaranteed, and dispatched experts to Okinawa to ensure a thorough investigation.

Representatives of the US military in Okinawa could not be reached for immediate comment yesterday.

More than half of some 47,000 American troops in Japan under a decades-long security alliance are stationed on Okinawa, the site of a major World War II battle that was followed by a 27-year US occupation of the island.

Islanders have complained for decades about noise and accidents.

In December, five crew members aboard a US Marine MV-22 Osprey were injured after what the Pentagon described as a "mishap" resulting in the plane landing in shallow waters off Okinawa.

Okinawa residents have protested against the deployment of Ospreys in Japan, after a series of accidents in other countries involving the hybrid aircraft.

AGENCE FRANCE-PRESSE