Qatar Airways raised eyebrows across the aviation industry this week when American Airlines announced the state-owned airline company had reached out to acquire at least a 10 percent stake in the U.S. company.

The overture, disclosed Thursday, sent American shares up 1.2 percent for the day. But in a letter to employees, American Airlines Chief Executive Doug Parker said he was puzzled by the Persian Gulf carrier's interest given the fact that the two airlines have been battling over the legitimacy of government subsidies.

"While anyone can purchase our shares in the open market, we aren't particularly excited about Qatar's outreach," Parker wrote.

American Airlines, Delta Airlines and United Airlines and their unions sent an open letter to President Trump in March asking him to enforce trade agreements with the United Arab Emirates and Qatar that are supposed to keep competition on a level playing field. The U.S. companies accuse Qatar Airways and Etihad Airways of operating with an unfair advantage by receiving large government subsidies from their native countries.

"Is this fake news?" asked Dennis Tajer, spokesman of the Allied Pilots Association, which represents American's pilots and wants trade agreements enforced. "The reaction was you have to be kidding me and why."

On its website, Qatar Airlines said it plans to make an initial investment of at least $808 million, or 4.75 percent in the company, which is the most American Airlines allows without advanced approval from its board. Earlier, the company suggested it would seek as much as a 10 percent stake.

"Qatar Airways sees a strong investment opportunity in American Airlines," the company said in the statement. "Qatar Airways believes in American Airlines' fundamentals and intends to build a passive position in the company with no involvement in management, operations or governance."

Daniel McKenzie, an American Airlines analyst for the Buckingham Research Group, said in a report that "the investment is somewhat awkward given the US airline industry's allegations of unfair trade practices by Middle Eastern carriers."

But Qatar Airways interest could be seen as a way to strengthen its relationship with a major source of revenue since the United States is Qatar's no. 1 destination and accounts for 8 percent of its overall flying, he wrote.

Tensions in the Persian Gulf could also play a role, analysts said. Qatar has been engaged in a diplomatic fight with next-door neighbor Saudi Arabia, which led Egypt, Bahrain and the United Arab Emirates to cut ties with Doha, the country's capital, over claims it supports of extremist groups.

"They just got blocked from flying to four countries," said Samuel Engle, an aviation consultant and vice president at ICF. "Fourteen percent of their traffic came from those countries. Even if Qatar is able to repair that, that kind of event is a reminder that there is benefit to having a diversified portfolio."

If Qatar actually invests, time will tell if the bet works out. History is not on the airline's side.

"The history of minority investments in airlines that were strictly financial has not been very positive," Engle said. "There have been few success stories. The minority investment doesn't give you enough control with what your partner is doing. There's not a lot of airlines pursuing that strategy globally."