WASHINGTON — The White House 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 Trump administration said it had expelled eight immigrants convicted of violent crimes in the United States but refused to reveal where they would end up. The judge’s statement was a notably strong rebuke to the government’s attempts to manage immigration.

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 department actions in this case are unquestionably in violation of this court’s order,” Murphy said Wednesday, arguing that the deportees didn’t have “meaningful opportunity” to object to being sent to South Sudan. 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. 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.

“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.

Administration officials, who have repeatedly clashed with the courts over their attempts to deport large numbers of immigrants, made their displeasure clear Wednesday.

“It is absurd that an activist judge is trying to force the United States to bring back these uniquely barbaric monsters who present a clear and present threat to the safety of the American people,” Tricia McLaughlin, a department spokesperson, said in a statement after the press conference.

Homeland Security officials released few specific details about the deportation flight. They said it left Tuesday with eight people on board and said 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.

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 was the mistaken deportation of an immigrant 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.

The administration officials insisted that the deported men had received due process, but did not provide 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.

Trina Realmuto, the executive director of the National Immigration Litigation Alliance, asked the judge to return the individuals. “They are no less deserving of protection than any other human beings on this planet,” she said.

Murphy said he would try to find a “narrowly tailored” fix for the violation. And while not directly threatening anyone with charges, he did raise the prospect.

“Everyone who was involved in an illegal deportation,” the judge said, “risks criminal contempt.”

Attorneys for the migrants told the judge that immigration authorities may have sent as many as a dozen people from several countries to Africa. The lawyers say that violates a court order that people have a “meaningful opportunity” to argue that sending them to a country outside their homeland would threaten their safety.

The apparent removal of one man from the troubled Southeast Asian nation of Myanmar was confirmed in an email from an immigration official in Texas, according to court documents. He was informed only in English, a language he does not speak well, and his lawyers learned of the plan hours before his deportation flight, they said.