And Mexico's foreign ministry has sharply condemned what it has called "disproportionate use of lethal force in the exercising of immigration control functions" by U.S. Border Patrol agents.

Shortly after he was named as Mexico's new ambassador to the United States earlier this month, Eduardo Medina Mora said the issue of immigration reform was of "great interest" to the Mexican government, while noting that it was a complicated political issue in the United States.

"This is an issue on the internal political agenda of the United States. It is not an issue on the bilateral agenda. Nonetheless we have a very great interest, an unavoidable responsibility to defend the interests of our fellow citizens and to promote an argument that increases opportunities for them," Medina Mora told reporters.

For more than a decade, the Mexican government has played an active role advocating for millions of migrants abroad.

Shortly after taking office in 2000, then-President Vicente Fox met with migrants in his official residence and soon created a Cabinet-level position dedicated to Mexicans who were living in other countries. During his administration, Mexicans won the right to vote abroad in 2005 after a hard-fought legislative campaign.

And Mexican government officials have created matching programs aimed at using the money Mexicans sent home to fund public works projects south of the U.S.-Mexico border.

It's a significant shift in a country where emigrants were once treated as traitors abandoning their homeland. Now, it's common for Mexican officials to acknowledge emigrants' contributions, and to advocate on their behalf.

In a visit to the White House last year, Mexican President Enrique Pena Nieto said he supported Obama's push for immigration reform.

"More than demanding what you should do, I do want to tell you that we want to contribute," he said. "We really want to participate and we want to contribute toward the accomplishment, so we can participate in the betterment and well-being of so many people who live in your country."