The Trump administration has abruptly cleared out a second group of migrants it brought to the American 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 to discuss a sensitive issue, said it happened on Tuesday.
The move comes days before a Federal 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.
In late February, the administration abruptly emptied two detention sites the government had used to hold 177 Venezuelans flown in from the United States, including a military prison building formerly used to hold terrorism detainees.
But in moving those detainees on Feb. 20, the administration repatriated the migrants to the custody of their home government. This time, the officials said, the men were taken to an international airport in Alexandria, La.
The Homeland Security Department’s press office did not immediately respond to a request for comment.
The airport in central Louisiana, which services military and charter flights, has emerged as a hub of immigration detention activity. ICE has sent nearly 100 migrants there from Guantánamo, starting with 48 on March 2. One of them was sent to a processing center in Pine Prairie, about an hour south of the airport.
A prominent pro-Palestinian activist whom the Trump administration had arrested in New York was taken to another ICE facility in Louisiana, about an hour’s drive north of that airport. The administration is trying to deport the activist, Mahmoud Khalil, because he helped lead anti-Israel protests at Columbia University. His case has drawn attention because he is a permanent legal resident and because the attempt to deport him has raised free-speech issues.
As part of a broader effort to carry out mass deportations, President 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 cast the prison as a good holding facility for detainees deemed to be dangerous, like Venezuelans portrayed as being part of Tren de Aragua, a gang the administration has designated as a foreign terrorist organization.
The government has not presented evidence that the Venezuelans who spent time in Camp Six before being repatriated last month were members of that gang. Most of those whose identities are known do not have criminal records in the United States.
Regardless, the administration has yet to offer a detailed explanation for temporarily sending migrants to Guantánamo, including those who are not accused of being members of a dangerous gang.
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 Six.
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 Six. It said ICE staff 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.
Colonel Green acknowledged that the troops have found themselves in tense situations. On a single day, before the Venezuelans were deported, he said, prison staff 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.
The Pentagon bought the restraint chairs years ago to strap down wartime detainees on hunger strikes for forced feedings.
Civil liberties and immigrant rights groups have filed two lawsuits challenging Mr. Trump’s policy. One seeks a court order allowing detainees access to lawyers, including in-person visits. The other challenges the legality of such transfers, seeking to bar the government from sending 10 migrants detained on U.S. soil.
Both cases have been assigned to Judge Carl J. Nichols, a Trump appointee, who is expected to hear the case on Friday afternoon. Ahead of that confrontation, the Justice Department filed a brief on Monday arguing that the policy is lawful under the Immigration and Naturalization Act.
Immigrant law specialists have questioned the legal basis for the operation, arguing that the act does not authorize the government to transfer people to the soil of another, unrelated country without its consent. Nor, they said, does it provide authority to detain people outside the territorial United States, which appears to exclude Guantánamo.
But the Justice Department argued that the Immigration and Naturalization Act should be interpreted as providing authority for the operation. Among other things, it argued that the statute says the government can detain people in a government facility, and the base is such a place. It also compared their detention there to a deportation flight that lands in a middle country to refuel before traveling to its final destination.
Declarations accompanying the department’s brief also opened a window onto some of what has happened at the base.
One, by Juan Lopez Vega, the acting director for enforcement and removal operations at ICE’s Miami field office, whose purview includes Guantánamo, described a system for allowing detainees to call lawyers. He also said none of the 10 migrants cited in the A.C.L.U. lawsuit were at imminent risk of being sent to Guantánamo, and committed to not moving them there through March 17.
Another, by Colonel Green, said he had arrived at Guantánamo less than a month ago. He suggested that the military was still shouldering the bulk of responsibilities for the initiative, although the Homeland Security Department has contributed more staff to the 1,000-worker immigration operation than in its earliest days.
At Camp Six, the guard force operates on 12-hour shifts that each use 28 soldiers, two ICE agents and seven to eight contractors paid by the agency per shift, according to Colonel Green. At the medium-security prison, he said, the guards are all ICE officers or contractors.
Eric Schmitt and Hamed Aleaziz contributed reporting from Washington.
