American Airlines Inc (AAL) - Get Report has heated up its war of words against Qatar Airways in a regulatory filing that hits back at the Gulf carrier's plans to buy shares in the biggest U.S. airline.

American said Qatar Airways had revised its antitrust filing with U.S. regulators seeking clearance to buy up to a 10% stake in the carrier, but said no further details of the changes to the filing were given. American reiterated that the proposed investment was not solicited by American Airlines and would in "no way change the company's board composition, governance, management or strategic direction."

It also included strong language about the Open Skies agreement between the United Arab Emirates and Qatar which has seen major airlines accuse the Gulf states of unfairly subsidizing their government-run airlines.

"American Airlines continues to believe that the President and his administration will stand up to foreign governments to end massive carrier subsidies that threaten the U.S. aviation industry and that threaten American jobs," the filing said.

American also said that it would end a code-share agreement with Qatar Airways and Etihad Airways over the dispute, with the change meaning American will no longer sell tickets on aircraft operated by either Gulf carrier as if they were its own flights.

Qatar Airways CEO Akbar Al Baker was undaunted by the move, saying Thursday the stake purchase would go ahead despite American's resistance.

"Our stock purchase request and filing is going ahead as normal," al-Baker told reporters in Doha, according to Reuters. "We had to clarify certain questions of the regulator, which we compiled with."

Qatar Airways has also come under fire for remarks about the age of flight attendants on American carriers. During a speech to a small audience Qatar Airways CEO Akbar Al Baker said that the average age of flight attendants on his airline is 26 years of age, adding, "You know you're always being served by grandmothers on American Airlines."

Al Baker later apologized for the comment. "This is a time of strong rivalry between our airline and the U.S. carriers, and we are of course immensely proud of our own cabin crew."

"Cabin crew are the public face of all airlines, and I greatly respect their hard work and professionalism," he said. "They play a huge role in the safety and comfort of passengers, irrespective of their age or gender or familial status."

American shares shares were trading modestly higher in premarket trading Thursday after closing at $53.80 each last night in New York and have gained more than 11% since Qatar indicated its interest in buying a stake on June 22.

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