Qatar Airways announced on August 2 that it will not pursue an ownership stake in American Airlines in another sign of the deepening dispute between U.S. and Persian Gulf carriers. American Airlines recently notified both Qatar Airways and Etihad Airways of Abu Dhabi that it will discontinue its codesharing partnerships with them.

In June, Qatar Airways notified American Airlines of its interest in acquiring a 10-percent stake in the publicly traded U.S. carrier, an investment that American Airlines opposed. With its latest announcement, the Gulf carrier said it has dropped the proposal.

“Qatar Airways has taken the decision not to proceed with its proposed passive financial investment in American Airlines,” the carrier stated. “Further review of the proposed financial investment, taking into account the latest public disclosure of American Airlines, has demonstrated that the investment no longer meets our objectives.”

The Doha-based carrier said it will continue to investigate “alternative investment opportunities” in the U.S. and elsewhere.

American, Delta and United airlines since 2015 have waged a lobbying war against, Qatar, Etihad and Emirates airlines, alleging the latter state-owned carriers have benefited from $50 billion in government subsidies since 2004 in violation of Open Skies trade agreements. In July, seven U.S. senators wrote to Secretary of State Rex Tillerson and Transportation Secretary Elaine Chao, calling on the Trump administration to enforce those agreements with Qatar and UAE.

The Partnership for Open & Fair Skies, the lobbying group that represents the U.S. carriers, the Air Line Pilots Association and other labor groups claim that 285 members of Congress to date have spoken out against the alleged trade violations.

American Airlines referenced the dispute over Open Skies agreements in its late June decision to discontinue codeshare agreements with Qatar Airways and Etihad Airways. The Fort Worth, Texas-based carrier was diplomatic in responding to Qatar Airways' latest announcement.

“We respect Qatar Airways’ decision not to proceed with its proposed investment in American Airlines,” the carrier said in an emailed statement. “This in no way changes the course for American. Our 120,000 team members remain energized and focused on taking care of those who entrust us with their travel needs.”

In a Securities and Exchange Commission filing that it made in June after receiving notification of Qatar Airways’ interest in acquiring shares, American Airlines did raise the issue of the Open Skies dispute.

“The proposed investment by Qatar Airways was not solicited by American Airlines and would in no way change the company’s board composition, governance, management or strategic direction,” the carrier stated in the filing. “It also does not alter American Airlines’ conviction on the need to enforce the Open Skies agreements with the United Arab Emirates and the nation of Qatar and ensure fair competition with Gulf carriers, including Qatar Airways. 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.”