A US federal judge ruled on Friday that the Trump administration must return a Salvadoran migrant who was wrongly deported to a notorious prison in his home country.

The 29-year-old man was living in the state of Maryland. He was among a group of mostly-undocumented migrants who were deported to El Salvador on March 15.

US Justice Department lawyers admitted in court filings that the man had been deported due to an "administrative error."

The Salvadoran migrant is married to a US citizen. He lived in the country legally with a work permit.

'No dispute' of mistake

According to District Judge Paula Xinis, the Salvadorian man was detained "without legal basis" and deported "without further process or legal justification."

He was sent to El Salvador's notorious Terrorism Confinement Center (CECOT).

The judge ordered his US return no later than April 7, and said his presence in El Salvador "constitutes irreparable harm."

The US government's lawyer said that while there's "no dispute" that the man should not have been deported, the administration argued it has no legal authority to bring him back to the US.

The Salvadorian man's lawyers rejected this claim.

"They put him there, they can bring him back," a member of his legal team in a statement.

Judge Xinis agreed.

"Why can't the US get [him] back?" she asked.

The lawyer representing the US government saying he had asked the administration that question but had not received an answer that he found satisfactory.

Violation of court order?

The ruling was the latest legal setback for the Trump administration's deportation policies, as part of which three planeloads of migrants were deported to El Salvador last month over alleged ties to criminal gangs.

A judge in Washington said there is a "fair likelihood" the Trump administration violated the court decision that ordered the temporary blocking of the deportation of alleged Venezuelan gang members under a rarely invoked 18th-century law.

As the court had made the decision, the first two planes carrying the deportees were already on their way to El Salvador, with them continuing on their original route despite the court's decision.

Editor's note: DW follows the German press code, which stresses the importance of protecting the privacy of suspected criminals or victims and obliges us to refrain from revealing full names in such cases.

Edited by: Zac Crellin