FORT WORTH, Texas >> Delta Air Lines will be allowed to keep a route between the U.S. and Japan that was sought by American Airlines Group Inc., which is prepared to step in should the current carrier not provide daily service.

The U.S. Department of Transportation said Friday that Delta could retain the route between Seattle and Haneda International Airport in Tokyo but with more flights.

Atlanta-based Delta must fly the route daily and not go long stretches without scheduled service, the Dallas Morning News reported. DOT says Delta would lose the route to Fort Worth-based American if Delta doesn’t meet the requirements.

American last October argued DOT should transfer the route because Delta operated just enough flights to avoid triggering a 90-day dormancy ruling.

U.S. carriers, under an agreement with Japan, can operate four daily round-trip flights at Haneda, which is closer to downtown Tokyo than the city’s other major airport, Narita. That service is now provided by Delta from Los Angeles and Seattle; Hawaiian Airlines from Honolulu; and United Airlines from San Francisco.

“After an extensive review, the DOT concluded that Delta’s Seattle-Haneda service provides the best public use of the available slot pair between the U.S. and Haneda Airport,” Delta spokesman Trebor Banstetter said. The carrier earlier this month resumed its nonstop service between Seattle and Haneda after a temporary seasonal suspension, he said.

American spokesman Matt Miller says the DOT recognized the importance of daily, year-round service in the U.S.-Haneda market.

“American stands ready to provide that service to customers through our Los Angeles hub,” Miller said.