In one of several problems relating to Boeing's newest model in recent weeks, about 40 gallons of fuel spewed onto the taxiway in Boston, compelling the plane to cancel take-off and to return to the gate.

"The cause of the fuel leak in Boston was a faulty valve," a JAL spokesman said.

No reason was given for the valve's failure.

Due to the fault, fuel flowed from the centre tank to the left main tank, and when that tank filled up, it overflowed into a surge tank and out through a vent, the spokesman said.

The aircraft is now in Tokyo and out of service while being checked. No timetable was given for its return to service.

U.S. regulators are still investigating a battery fire on an identical JAL-operated Boeing jet, which damaged the plane and an equipment bay also at Boston airport, 24 hours before the fuel leak.

Boeing defended the 787 Dreamliner on Wednesday, saying it was safe to fly. (Reporting by James Topham; Writing by Tim Hepher; Editing by Bernadette Baum)

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