WASHINGTON (Reuters) - Roughly one in 10 migrants pushed back to Mexico to await U.S. court hearings under a Trump administration program have been caught crossing the border again, a top border official said on Thursday.

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Acting U.S. Customs and Border Protection Commissioner Mark Morgan said during a White House briefing that migrants returned to Mexico under a program known as the Migrant Protection Protocols (MPP) have a 9% recidivism rate. Many of those migrants intend to seek asylum in the United States.

“Unfortunately, some of the individuals in the MPP program are actually going outside the shelter environment,” Morgan said. “They’re re-engaging with the cartels because they’re tired of waiting. And that’s when we’re hearing that some of that further abuse and exploitation is happening.”

Nearly 59,000 migrants have been returned to Mexico under the program, according to a CBP spokesman.

The administration of Republican President Donald Trump launched the MPP program in January as part of a strategy to deter mostly Central American families from trekking to the U.S. border to seek asylum. Trump officials have argued the bulk of such claims for protection lack merit and that migrants are motivated by economic concerns.

Immigration advocates say asylum seekers sent to wait in Mexican border towns, for the weeks or months it takes for their cases to wind through backlogged immigration courts, face dangerous and possibly deadly conditions.

Migrants who claim fear of returning to Mexico can ask to stay in the United States for the duration of their court case. But just 1% of cases have been transferred out of the program, according to a Reuters analysis of federal immigration court data as of early October.

A report released by the office of Democratic U.S. Senator Jeff Merkley on Thursday criticized the MPP program and the Trump administration’s handling of a migrant surge earlier this year.

The report, citing interviews with U.S. Citizenship and Immigration Services employees, said political supervisors at the agency intervened to override asylum officer decisions to remove migrants from the MPP program.

An agency spokeswoman called the allegation “completely false” and said political appointees do not conduct reviews of such decisions.

Border Patrol arrested 35,444 people in October, the fifth consecutive monthly decline this year, according to a CBP official. The administration has said the MPP program and other measures have helped lead to a decline in border arrests.”