United Airlines CEO Oscar Munoz said in a statement on Wednesday that the airline had told the US government not to use its planes to fly children who have been separated from their families by immigration officials at the US-Mexico border.

Hours earlier, American Airlines made a similar announcement.

Major US airlines are under contract with the US government to provide transportation services.

United Airlines said in a statement on Wednesday that it had informed the US government that it should not use its planes to fly children who have been separated from their families by immigration officials at the US-Mexico border.

"Our company's shared purpose is to connect people and unite the world," United's CEO, Oscar Munoz, said in the statement. "This policy and its impact on thousands of children is in deep conflict with that mission and we want no part of it."

Munoz is also one of the highest-profile Mexican-American CEOs in the world.

Hours earlier, American Airlines made a similar announcement. The Texas-based carrier said: "The family separation process that has been widely publicized is not at all aligned with the values of American Airlines — we bring families together, not apart."

American Airlines, United, and several other major US carriers are under contract with the government to provide transportation services for myriad purposes, including employee work trips and even deportations.

American and United said in their statements that they could not find any evidence that immigrant children separated from their families had been flown on their planes.

In recent weeks, outcry has grown over the treatment of immigrants attempting to cross the US-Mexico border, including the forced separation of children from their parents and the use of large holding facilities along the border.

On Wednesday, the Trump administration indicated it was working on an executive order to keep immigrant families from being separated.

Here is Munoz's statement in its entirety:

"At United Airlines, we have been concerned about reports that commercial airlines have been used to transport immigrant children separated from their parents by a newly implemented immigration enforcement policy. Based on some research we have done internally and public reports, we have not seen evidence these children have been flown on United aircraft.

"Based on our serious concerns about this policy and how it's in deep conflict with our company's values, we have contacted federal officials to inform them that they should not transport immigrant children on United aircraft who have been separated from their parents. Our company's shared purpose is to connect people and unite the world. This policy and its impact on thousands of children is in deep conflict with that mission and we want no part of it."