WASHINGTON — The Trump administration violated a court order on deportations to third countries with a flight linked to the chaotic African nation of South Sudan, a federal judge said Wednesday, hours after the administration said it had expelled eight migrants convicted of violent crimes in the United States but refused to reveal where they would end up.

In an emergency hearing he called to address reports that immigrants had been sent to South Sudan, Judge Brian E. Murphy in Boston said the eight migrants aboard the plane were not given a meaningful opportunity to object that the deportation could put them in danger. Minutes before the hearing, administration officials accused “activist judges” of advocating the release of dangerous criminals.

The group was flown out of the United States just hours after getting notice, leaving them no chance to contact lawyers who could object in court.

Government attorneys argued that the men had a history with the immigration system, giving them prior opportunities to express a fear of being deported to a country outside their homeland. They also said that immigration authorities may have misunderstood the order because the judge did not specify the time needed between notice and deportation.

The migrants’ home countries — Cuba, Laos, Mexico, Myanmar, Vietnam and South Sudan — would not take them back, according to Todd Lyons, the acting director of Immigration and Customs Enforcement who spoke to reporters in Washington just before the court hearing. He later said the migrants either came from countries that often do not take back all their deported citizens or had other situations that meant they could not be sent home.

‘Security threats’

“These represent the true national security threats,” Lyons said at a news conference. Behind him was a display of photos of men he said had been convicted of rape, homicide, armed robbery and other crimes.

President Donald Trump and Homeland Security Secretary Kristi Noem “are working every single day to get these vicious criminals off of American streets — and while activist judges are on the other side, fighting to get them back onto the United States soil,” said Tricia McLaughlin, a department spokesperson.

Homeland Security officials released few specific details about the deportation flight. They said the flight left Tuesday with eight people on board and that they remained in the department’s custody Wednesday. Officials said they could not disclose the migrants’ final destination because of “safety and operational security.”

The case comes amid a sweeping immigration crackdown by the Republican administration, which has pledged to deport millions of people who are living in the United States illegally. The legal fight is the latest flashpoint as the administration rails against judges whose rulings have slowed the president’s policies.

Lawsuits galore

With Congress largely silent or supportive, opponents of Trump’s agenda have filed hundreds of lawsuits and judges have issued dozens of orders against the administration. Immigration has been the most contentious issue. There is the mistaken deportation of an immigration who was living in Maryland to a prison in El Salvador, as well as Trump’s push to swiftly deport alleged Venezuelan gang members without a court review.

“We see activist judges stepping in in a way that we have never seen before, to put criminals first and not the American people,” Madison Sheahan, the ICE deputy director, said.

The administration officials insisted that the men had received due process, but did not provide any details. Immigration rights lawyers have said that the deportations violated a court order against sending people to countries other than their homelands without first allowing them to argue the removal could put them in danger. Murphy had ruled Tuesday that the administration must retain custody and control of those “currently being removed to South Sudan or to any other third country, to ensure the practical feasibility of return” if he founds such removals were unlawful.