United Airlines CEO Scott Kirby confirmed Monday that he approached American Airlines to explore a possible merger between the two carriers, a move that sparked concerns about competition in the airline industry.

"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 said in an April 27 statement.

The United CEO previously floated the idea of a merger to Trump administration officials, according to sources familiar with the situation, in a conversation that came to light earlier this month. 

American dismissed the idea of talks with United, saying in an April 17 statement that it is "not engaged with or interested" in any merger discussions.

"I was hoping to pitch that story to American, but they declined to engage and instead responded by publicly closing the door. And without a willing partner, something this big simply can't get done," Kirby said Monday.

United and American didn't immediately return requests for comment.

The United CEO has previously hinted at an expansion. However, any merger would face tough regulatory scrutiny. 

Lawmakers were quick to criticize the potential of a United-American combination. In a letter to the airline CEOs last week, Sen. Elizabeth Warren, a Democrat from Massachusetts, and Sen. Mike Lee, a Utah Republican, said such a move would weaken industry competition and harm consumers.

In his statement on Monday, Kirby laid out his argument for the merger, saying it would create "high-paying, unionized jobs," offer more affordable flying options for customers and allow the airline to compete with foreign carriers.

"By combining our airlines and using that scale to revolutionize our customers' experience, we'd create a new, thriving U.S. airline that would be the very best in the world for customers – full stop," he said.