WASHINGTON – Lithium batteries that can leak corrosive fluid and start fires have emerged as the chief safety concern involving Boeing's 787 Dreamliner, a problem that apparently is far more serious than government or company officials acknowledged less than a week ago.

The Federal Aviation Administration late Wednesday grounded Boeing's newest and most technologically advanced jetliner until the risk of battery fires is resolved. The order applies only to the six Dreamliners operated by United Airlines, the lone U.S. carrier with 787s. Other airlines and civil aviation authorities in other countries quickly followed suit.

Japan's two largest air carriers voluntarily grounded their 787s on Wednesday ahead of the FAA's order following an emergency landing by one of the planes in Japan. On Thursday, the European Aviation Safety Agency ordered all European carriers to ground the jetliner. The Indian government ordered Air India to ground its fleet of six Boeing 787s, and Ethiopian Airlines grounded its four 787s "for precautionary inspection."