More than 200 Venezuelans alleged by the White House to be gang members have been deported from the US to a supermax prison in El Salvador, even as a US judge blocked the removals.

El Salvadoran President Nayib Bukele wrote on social media that 238 members of the Venezuelan gang Tren de Aragua had arrived in the Central American country, along with 23 members of the international MS-13 gang, on Sunday morning.

Neither the US government nor El Salvador has identified the detainees, nor provided details of their alleged criminality or gang membership.

A federal judge's order prevented the Trump administration from invoking a centuries-old wartime law to justify some of the deportations, but the flights had already departed.

"Oopsie... Too late," posted Bukele on social media, referring to the judge's ruling.

A video attached to one of his posts shows lines of people with their hands and feet shackled being escorted by armed officials from the planes.

White House press secretary Karoline Leavitt denied the court ruling had been violated.

"The administration did not 'refuse to comply' with a court order," she said.

"The order, which had no lawful basis, was issued after terrorist TdA [Tren de Aragua] aliens had already been removed from US territory."

US President Donald Trump announced on Saturday that he had signed a proclamation invoking the Alien Enemies Act of 1798 as he accused Tren de Aragua of "perpetrating, attempting, and threatening an invasion of predatory incursion against the territory of the United States".

He said members of the gang would be deported for engaging in "irregular warfare" against the US. The Alien Enemies Act was last used during World War II to intern Japanese-American civilians.

On Saturday evening, US District Judge James Boasberg in Washington DC ordered a 14-day halt to deportations covered by Trump's proclamation, pending further legal arguments.

After lawyers told him that planes with deportees had already taken off, Judge Boasberg gave a verbal order for the flights to turn back, US media reported, although that directive did not form part of his written ruling.

The written notice appeared in the case docket at 19:25 EDT on Saturday (00:25 GMT on Sunday), the Reuters news agency reports, although it is unclear when the flights carrying the alleged gang members departed from the US.

In a court filing on Sunday, Department of Justice lawyers said the order had not applied because the deportees "had already been removed from United States territory".

A senior administration official told CBS News, the BBC's US partner, that 261 people were deported on Saturday, 137 of whom were removed under the Alien Enemies Act over alleged gang ties.

The justice department has appealed against the judge's ruling.

The American Civil Liberties Union, which was involved in the lawsuit against the Trump administration, said the court's order may have been violated.

The case raises constitutional questions since, under the US system of checks and balances, government agencies are expected to comply with a federal judge's ruling.

Venezuela criticised Trump invoking the Alien Enemies Act, saying it "unjustly criminalises Venezuelan migration" and "evokes the darkest episodes in the history of humanity, from slavery to the horror of the Nazi concentration camps".

Rights groups condemned Trump, accusing him of using a 227-year-old law to circumvent due process.

Amnesty International USA wrote on X that the deportations were "yet another example of the Trump administration's racist targeting" of Venezuelans "based on sweeping claims of gang affiliation".

President Bukele, a Trump ally, wrote that the detainees were immediately transferred to El Salvador's notorious mega-jail, the Terrorism Confinement Center (Cecot).

The El Salvadoran president said they would be held there "for a period of one year", and that could be "renewable".

El Salvador's Cecot jail is part of Bukele's effort to crack down on the country's organised crime.

The newly built maximum-security facility, which can hold up to 40,000 people, has been accused by human rights groups of mistreating inmates.

The arrangement between the US and El Salvador is a sign of strengthening diplomatic ties.

El Salvador was the second country that Rubio visited as the US's top diplomat.

During that trip, which took place in February, Bukele made an initial offer to take US deportees, saying it would help pay for the massive Cecot facility.

The latest deportations under Trump's second term are part of the president's long-running campaign against illegal immigration in the US.

In January, Trump signed an executive order declaring Tren de Aragua and MS-13 foreign terrorist organisations.

He won over voters on the campaign trail, in part, by promising to enact the largest deportation operation in US history.

While illegal border crossings have plummeted to the lowest number in decades since Trump took office, the Republican president has reportedly been frustrated by the relatively slow pace of deportations so far.