San Salvador, El Salvador - A group of NGOs in El Salvador on Friday asked the Supreme Court to rule that the jailing of over 200 Venezuelan migrants at the request of the US was unconstitutional.

On March 15, President Donald Trump's administration flew 238 undocumented Venezuelans from the US to El Salvador, where President Nayib Bukele made a show of having them thrown in a notorious prison for gang members.

The Trump administration claimed that most of the deportees were members of the Venezuelan gang Tren de Aragua, which has a presence in the US.

The lawyers and families of several of the deported people have roundly denied the claim, saying they had committed no crimes and were designated as gang members merely on the basis of their tattoos.

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Rights activist Marisela Ramirez accused Bukele's government of "blatantly violating the fundamental rights" of the Venezuelans, noting they had not been tried and convicted of any crime in El Salvador.

Speaking to reporters, she also argued that the jailing of migrants deported from the US had no basis in law, as the government had not sought the approval of parliament.

A law firm hired by Venezuela has also launched legal action in El Salvador to try secure the release of the prisoners.

The Trump administration caused a furor by invoking a little-known 1798 wartime act to justify the summary deportations of the Venezuelans as part of a program of mass deportations.

On Friday, a US federal judge ordered the return to the US of a Salvadoran migrant who was mistakenly deported with the group.

Justice Department lawyers admitted in court filings that Kilmar Abrego Garcia (29), who is married to a US citizen, had been deported due to an "administrative error."

The White House argues that the US has no authority to force El Salvador to hand him back.