TOKYO (AFP) - French electrical system giant Thales has joined a Japan-US probe into a battery fire which forced a Boeing 787 Dreamliner to make an emergency landing in Japan, officials said today.

Two Thales engineers have been taking part in a CT scan of the aircraft's lithium-ion battery at a Japan space agency facility in Tokyo since Tuesday, said a Japan Transport Safety Board (JTSB) spokeswoman.

"They are participating as advisers to the BEA (the French civil aviation authority)," she said.

Thales designed the Dreamliner's electrical system and commissioned Japanese firm GS Yuasa to produce the next-generation aircraft's batteries.

A fire risk from overheating powerpacks emerged as a major concern after pilots were forced to land a domestic All Nippon Airways (ANA) flight in western Japan on Jan 16 due to smoke apparently linked to the plane's battery.

Investigators on Friday released a picture showing the blackened remains of the battery in the ANA plane.

JTSB and the US National Transportation Safety Board (NTSB) were expected to wrap up the scan of the burned battery later today, the spokeswoman said.

Engineers from GS Yuasa were also taking part in the probe.

The battery was expected to be dismantled and examined later.

Boeing's fuel-efficient planes suffered a series of problems earlier this month, prompting a global alert from the US Federal Aviation Administration that has seen all 50 operational Dreamliners grounded since last week.

Thales and GS Yuasa were also taking part in a separate investigation, led by the NTSB, into the cause of a fire on a Japan Airlines 787 Dreamliner in Boston on Jan 7.

US investigators probing that incident ruled out overheating as the cause, but the NTSB was still testing the charger and components linked to the battery.