The US Supreme Court handed Donald Trump a victory on Monday by letting him use a 1798 law that historically has been employed only in wartime to swiftly deport alleged Venezuelan gang members as part of the Republican president's hardline approach to immigration.

The court granted the administration's request to lift Washington-based US Judge James Boasberg's March 15 order that had temporarily blocked the summary deportations under Trump's invocation of the Alien Enemies Act while litigation in the case continues.

Trump invoked the Alien Enemies Act on March 15 to swiftly deport the alleged members of the Tren de Aragua gang, attempting to speed up removals with a law best known for its use to intern Japanese, Italian and German immigrants during World War Two.

In a legal challenge handled by the American Civil Liberties Union, a group of Venezuelan men in the custody of US immigration authorities on the same day sued on behalf of themselves and others similarly situated, seeking to block the deportations. They argued, among other things, that Trump's order exceeded his powers because the Alien Enemies Act authorises removals only when war has been declared or the United States has been invaded.

The Alien Enemies Act authorises the president to deport, detain or place restrictions on individuals whose primary allegiance is to a foreign power and who might pose a national security risk in wartime.

Boasberg, an appointee of Democratic President Barack Obama, temporarily blocked the deportations. But Trump's administration allowed two planes already in the air to continue to El Salvador where American officials handed 238 Venezuelan men over to Salvadoran authorities to be placed in the Central American country's "Terrorism Confinement Center."

The judge also has scrutinized whether the Trump administration violated his order by failing to return the deportation flights after his order was issued. Justice Department lawyers said the flights had left US airspace by the time Boasberg issued a written order and thus were not required to return. They dismissed the weight of Boasberg's spoken order during a hearing two hours earlier calling for any planes carrying deportees to be turned around.

Trump's administration has argued that Boasberg's temporary ban encroached on presidential authority to make national security decisions.

On March 18, Trump called for Boasberg's impeachment by Congress - a process that could remove him from the bench - drawing a rebuke from the US Chief Justice John Roberts. Trump on social media called Boasberg, who was confirmed by the US Senate in 2011 in a bipartisan 96-0 vote, a "Radical Left Lunatic" and a "troublemaker and agitator."

The DC Circuit upheld Boasberg's order after holding a contentious hearing that involved heated language. Judge Patricia Millett told Justice Department lawyer Drew Ensign that "Nazis got better treatment under the Alien Enemies Act than has happened here." Ensign responded, "We certainly dispute the Nazi analogy."

Family members of many of the deported Venezuelan migrants deny the alleged gang ties. Lawyers for one of the deportees, a Venezuelan professional soccer player and youth coach, said US officials had wrongly labelled him a gang member based on a tattoo of a crown meant to honour his favourite team, Real Madrid. (Reuters)