United Airlines CEO Scott Kirby on Monday outlined why he thinks a merger between his airline and rival American would benefit travelers, despite American's refusal to engage in negotiations.

"I was confident that this combination, which would have been about adding and not subtracting, creating a truly great airline that customers love, could get regulatory approval," Kirby wrote in a press release. "I was hoping to pitch that story to American, but they declined to engage and instead responded by publicly closing the door."

The stocks of both airlines soared two weeks ago when reports surfaced that Kirby had floated the idea of combining two of the biggest U.S. airlines to the White House. Kirby said Monday that he had approached American directly about a tie-up, but it's unclear whether that was before or after the White House meeting.

Days after the meeting in Washington, American shot down the idea of a merger.

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"American Airlines is not engaged with or interested in any discussions regarding a merger with United Airlines," the company said in an April 17 press release. Additionally, a combination of the two carriers "would be negative for competition and for consumers" and possibly raise antitrust concerns, the company said.

Fort Worth, Texas-based American Airlines is itself the product of a 2013 merger with US Airways Group.

President Donald Trump also said last week that he was against a merger of the airlines.

In his press release Monday, Kirby argued that a merger between the iconic airlines would expand service, create a globally competitive airline and boost the U.S. economy by creating millions of jobs and strengthening the aircraft manufacturing sector.

Shares of Chicago-based United shares fell 1.4% on Monday, to $91.72. They are down about 20% since the war in Iran began in late February, sending fuel prices soaring. American shares were down 2% in morning trading Monday, to $11.84. American is down about 15% since the war began.