U.S. border agents have expelled more than 200 non-Mexican unaccompanied children to Mexico, potentially violating U.S. laws and a diplomatic agreement with the country, according to a report by The New York Times.

The report is based partly on emails allegedly written by a top border official, Border Patrol Assistant Chief Eduardo Sánchez, warning that the expulsions violate U.S. policy and could endanger the Trump administration's entire quick deportation strategy.

“Recently, we have identified several suspected instances where Single Minors (SM) from countries other than Mexico have been expelled via ports of entry rather than referred to ICE Air Operations for expulsion flights,” Sánchez wrote in an email obtained by the Times.

If confirmed, the report would provide evidence for claims made by many immigration and border activists, who regularly accuse border authorities of cutting corners and violating internal and external regulations.

"Human rights advocates and government watchdogs have long accused Border Patrol of repeated failure to follow basic rules for the protection of children and migrants," said Aaron Reichlin-Melnick, policy counsel at the American Immigration Council.

"The agency has long struggled with a culture that views rules to protect migrants as somehow soft and contrary to the agency's militaristic ethos," said Reichlin-Melnick.

Customs and Border Protection (CBP) officials did not immediately return a request for comment on this story.

Apart from violating policy and an international agreement, summary expulsions of unaccompanied minors would imply that U.S. authorities have sent children alone into Mexico's border cities, where kidnapping and human trafficking are major criminal concerns.

The reported expulsions of unaccompanied minors come as the Trump administration has tweaked U.S. border policy to quickly expel migrants caught at the border.

Over the past year, the Trump administration has interpreted a Centers for Disease Control and Prevention (CDC) order as allowing agents to quickly expel undocumented immigrants caught at the border, streamlining that process.

The CDC order expulsions, known as Title 42 expulsions, have quickly become the preferred method of deportation used by CBP at the border — out of 54,771 undocumented immigrants encountered by CBP at the southwest border in September, 48,327 were processed and expelled under Title 42.

And a diplomatic agreement with Mexico has allowed CBP to return Central American asylum-seekers to Mexico while they await adjudication of their cases in U.S. courts.

But Mexico explicitly declined to receive unaccompanied minors from third countries.

In his email, Sánchez warns that violating the third-country minor policy could endanger implementation of the streamlined processes touted by Trump officials.

“Please note that if not corrected, these actions will place Title 42 operations in significant jeopardy and must be ceased immediately. To reiterate, under no circumstances should a SM from a country other than Mexico be knowingly expelled to Mexico,” wrote Sánchez.

According to the Times, Border Patrol Rio Grande Sector Chief Brian Hastings acknowledged some non-Mexican children had been sent into Mexico, and acting CBP Commissioner Mark Morgan said in a separate interview such expulsions would violate the agreement with Mexico.

The administration has been under fire, a week before Election Day, for failure to keep track of all of the children and parents separated as part of the family separation practice early on in Trump's tenure.