MEXICO CITY (Reuters) - Mexico's incoming ambassador to the United States on Tuesday slammed U.S. President Donald Trump's treatment of its southern neighbor as "unacceptable" and called for a migration mechanism to avoid illegal crossings by Mexicans to the United States.

Geronimo Gutierrez, who will be Mexico's third ambassador to the United States in less than a year, was speaking at a hearing in Mexico's Senate.

"The treatment received by our country is unacceptable and clearly not favorable," he said. "Trump and his government deserve respect and they will get it in so far as its reciprocal."

Gutierrez did not provide further details about the migration mechanism.

The U.S. government released guidelines on Tuesday showing almost all undocumented migrants will be subject to deportation, but protections will be left in place for "dreamers" who entered the country illegally as children.

Gutierrez, who is expected to be ratified by the Mexican Senate this week, held senior posts in the two previous administrations headed by the opposition center-right National Action Party (PAN).

(Reporting by Anahi Rama; Writing by Christine Murray; Editing by Richard Chang)