A US appeals court denied on Wednesday a bid by the Trump administration to lift a lower court order barring summary deportations of Venezuelan migrants using an obscure wartime law.

A three-judge panel of the US Court of Appeals voted 2-1 to temporarily keep in place the ban on deportations carried out under the 1798 Alien Enemies Act.

President Donald Trump sent two planeloads of alleged members of the Venezuelan gang Tren de Aragua to a prison in El Salvador on March 15 after invoking the AEA, which has only been used previously during the War of 1812, World War I and World War II.

District Judge James Boasberg issued a restraining order that same day, temporarily barring the administration from carrying out any further deportation flights under the AEA, which the Justice Department appealed to remove.

Attorneys for several of the deported Venezuelans have said that their clients were not members of Tren de Aragua, had committed no crimes and were targeted largely on the basis of their tattoos.

Judge Patricia Millett, an appointee of Democratic president Barack Obama, and Judge Karen Henderson, an appointee of Republican president George H.W. Bush, voted to keep the temporary ban on deportations using the AEA in place.

The third judge on the panel, Justin Walker, a Trump appointee, dissented.

Millett said the Venezuelan migrants had been deported based on the government?s allegations alone ?with no notice, no hearing, no opportunity- zero process- to show that they are not members of the gang.?

?If the government can choose to abandon fair and equal process for some people, it can do the same for everyone,? she said.

Homeland Security Secretary Kristi Noem visited the prison in El Salvador on Wednesday where the Venezuelans are being held.

Noem said on social media before her arrival that she would be meeting Salvadoran President Nayib Bukele to discuss how the United States ?can increase the number of deportation flights and removals of violent criminals from the US.?

During a hearing on Monday at which the government sought to have the court order lifted, Justice Department attorney Drew Ensign said it ?represents an unprecedented and enormous intrusion upon the powers of the executive branch? and ?enjoins the president?s exercise of his war and foreign affairs powers.?

Millett for her part said ?Nazis got better treatment? from the United States during World War II under the AEA.

Lee Gelernt, a lawyer for the American Civil Liberties Union, which filed suit against the deportations along with other rights groups, welcomed the appeals court move.

?The decision means that hundreds of individuals remain protected from being sent to a notorious black-hole prison in a foreign country, without any due process whatsoever,? Gelernt said.

Skye Perryman, president of Democracy Forward, said, ?President Trump is bound by the laws of this nation, and those laws do not permit him to use wartime powers when the United States is not at war and has not been invaded.?

Boasberg, the district court judge, has said migrants subject to potential deportation under the AEA should be ?entitled to individualized hearings to determine whether the Act applies to them at all.?

Trump has repeatedly lashed out at Boasberg, even going so far as to call for his impeachment, a remark that drew a rare public rebuke from Supreme Court Chief Justice John Roberts.

In his latest outburst, Trump said on Thursday that Boasberg was ?highly conflicted? and called for an investigation into a court system that was, he said was ?rigged? against him.

The contentious case has raised concerns among legal experts that the administration may potentially ignore the court order, triggering a constitutional crisis.(AFP)

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