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GUANTÁNAMO BAY, Cuba — The Trump administration has abruptly cleared out a second group of migrants it brought to the U.S. military base at Guantánamo Bay, Cuba, returning to the United States 40 men it had flown there in the past few weeks, according to officials familiar with the matter.

The government has not announced that it relocated the men to one or more Immigration and Customs Enforcement facilities in Louisiana nor was the reason for the move clear. But the officials familiar with the matter, speaking on the condition of anonymity, said it happened Tuesday.

The move comes days before a U.S. District Court judge in Washington is set to hear a major challenge to aspects of the policy.

It is the second time the administration has brought people to Guantánamo Bay only to remove them after a few weeks, a costly and time-consuming exercise.

The Homeland Security Department’s press office did not immediately respond to a request for comment.

As part of a broader effort to carry out mass deportations, President Donald Trump ordered the Defense and Homeland Security departments to prepare to send migrants to Guantánamo a week after taking office. As of Friday, according to a court filing this week, 290 migrants from 27 countries have since cycled through the base.

The administration has yet to offer a detailed explanation for temporarily sending migrants to Guantánamo.

As of Friday, the court filing said, 17 migrants were being held in a medium-security facility, a dormitory-style building on the other side of the base from the wartime prison, while 23 were in Camp 6.

Another court filing this week, a declaration by the Army officer in charge, Lt. Col. Robert Green, offered some details of how detainees have been treated at Camp 6. It said ICE staff members watch as U.S. troops conduct strip searches on migrants newly brought there as “high-threat illegal aliens.” After that, he said, migrants are patted down when moved from cells.

Green acknowledged that the troops have found themselves in tense situations. On a single day, before the Venezuelans were deported, he said, prison staff members strapped six migrants into restraint chairs or a medical stretcher after each man undertook a so-called self-harm episode — military jargon for a suicide threat, gesture or attempt.