A US appeals court judge on Monday said the US gave Nazis "better treatment" during World War II than it did to hundreds of Venezuelans deported this month over alleged gang ties.

The US Court of Appeals for the DC Circuit heard arguments over the Trump administration's use of the 1798 Alien Enemies Act to deport 238 alleged Venezuelan gang members to a mega-prison in El Salvador.

During a fraught two-hour hearing, Judge Patricia Millett questioned the government's use of the law to deport the Venezuelans without a way to challenge the allegations.

"There were planeloads of people," she said. "Nazis got better treatment under the Alien Enemy Act than has happened here."

Earlier on Monday, a federal judge refused to lift a temporary restraining order blocking the Trump administration from deporting Venezuelan migrants with the invocation of the wartime powers.

Judge James Boasberg ruled that many of those deported dispute their gang affiliation and must be allowed to challenge their removal.

Trump proclaimed on 15 March that members of the Venezuelan crime gang Tren de Aragua were "conducting irregular warfare" against the US, justifying their deportation under the Alien Enemies Act of 1798.

But later that evening, Judge Boasberg issued a 14-day halt to deportations under the proclamation, verbally ordering the government to turn flights around. The White House insisted it was too late, as the planes were already in international airspace.

In a hearing on Monday, lawyers for the government sought to overturn Boasberg's original March 15 restraining order.

Government lawyer Drew Ensign called Boasberg's temporary restraining order "utterly unprecedented" and argued it intruded upon the president's foreign policy powers.

He added that the government "certainly dispute[d] the Nazi analogy" Judge Millett gave.

The claims sparked a tense back-and-forth between Mr Ensign and the judge, who argued: "Of course there's no precedent, because no president has ever used this."

"Y'all could've picked me up on Saturday and thrown me on a plane thinking I'm a member of Tren de Aragua and given me no chance to protest it," added Judge Millett, an appointee of former President Barack Obama.

She claimed the administration did not carefully review whether the Venezuelan nationals actually were gang members before they were deported.

Later on Monday, border czar Tom Homan called the Nazi-related allegation "disgusting", according to CBS, the BBC's news partner.

US Circuit Judge Justin Walker, an appointee of Trump, appeared less skeptical of the government's arguments. The three-judge panel did not say when it would rule on the issue.

The Trump administration has maintained that the Venezuelan men were "carefully vetted" and verified as gang members before being flown to El Salvador.

But some of their family members have disputed that allegation, and US officials have acknowledged "many" of the men have no US criminal record.

On Monday before the hearing, Judge Boasberg noted: "Because the named Plaintiffs dispute that they are members of Tren de Aragua, they may not be deported until a court has been able to decide the merits of their challenge."

The judge noted the Trump administration was still free to deport Venezuelans through regular immigration process.

The deportations have created tension between the White House and Judge Boasberg, who said on Friday that he had never heard lawyers for the government speak to him the way the Trump administration attorneys had.

"I will get to the bottom of whether they violated my order, who ordered this and what the consequences will be," the judge said at a hearing last Friday.

Trump has described Boasberg as a "constitutional disaster" who "doesn't mind if criminals come into our country".

The Alien Enemies Act grants the president sweeping powers to quickly deport citizens of an "enemy" nation.

The deportations have been criticised by human rights groups, which have argued the move is illegal because the US is not at war.

Speaking to Fox News on Sunday, Trump's Attorney General Pam Bondi defended the government's use of the war-time law to ship the Venezuelan nations to El Salvador.

"It's modern-day warfare, and we are going to continue to fight that and protect American citizens every single step of the way," Bondi told Fox News.