TOKYO — Japan Airlines, wooed for months by Delta Air Lines with promises of cash and a broad global network, spurned the world's biggest carrier and opted to keep its alliance with American Airlines.

The Japanese carrier said today it will strengthen its partnership with American, and the two airlines will jointly seek antitrust immunity on trans-Pacific routes.

The decision brings to an end a fierce tug-of-war over Japan's ailing flagship carrier, which is restructuring under bankruptcy but offers the U.S. airlines access to lucrative Asian routes.

In an aggressive courtship, Delta and its partners offered JAL $1 billion. American and its partners said they would give JAL as much as $1.4 billion to stay. Delta in a statement didn't directly address JAL's choice, instead asserting it remains a big player in Asia.

American's victory seemed improbable a few weeks ago when Japanese officials, convinced of the long-term revenue benefits, were pushing JAL toward Delta and its SkyTeam partners. But new JAL chairman Kazuo Inamori insisted that management would re-evaluate both proposals.

JAL's loyalties swung back to American in the end as executives decided an alliance switch would do more harm than good during a restructuring that is expected to take three years.