A wrongly deported Salvadoran man sent back to the United States during a fierce row over President Donald Trump's hardline immigration policies has been released from prison, where he had been detained on human smuggling charges.

The release on Friday came after the US Supreme Court had ordered the Trump administration to "facilitate" the return of Kilmar Abrego Garcia after the government admitted it had mistakenly sent him to a notorious maximum security prison in El Salvador in March.

He was returned in June, and then quickly arrested and charged with trafficking undocumented migrants. His release from prison in Tennessee on Friday was ordered by a judge.

Migrant rights organisation Casa released a statement quoting Abrego Garcia as saying it was a "very special day" after seeing his family for the first time in more than 160 days.

"We are steps closer to justice, but justice has not been fully served," the Salvadoran said, according to CASA, which hailed him as a "symbol of strength, resistance and hope."

The case has become emblematic of Trump's crackdown on illegal migration.

Right-wing supporters praise the Republican president's toughness, but legal scholars and human rights advocates have blasted what they say is a haphazard rush to deport people in violation of basic US laws.

Abrego Garcia's attorney Sean Hecker, who earlier confirmed that his client was heading home to the eastern US state of Maryland, accused Trump's government of a "vindictive attack on a man who had the courage to fight back against the administration's continuing assault on the rule of law."

Hecker said his client was "grateful that his access to American courts has provided meaningful due process."

But the saga may not be over for the Salvadoran, who is married to a US citizen.

The Trump administration is not barred from initiating "lawful immigration proceedings upon Abrego Garcia's return to Maryland" – provided it gives 72 hours' notice before deporting him to a third country – under a July federal court ruling.

Multiple US media outlets reported that the Department of Homeland Security had notified his legal team that he had been ordered to report to immigration officials in Baltimore on Monday, and may be sent to the East African nation of Uganda.

The department did not immediately reply to a request for comment on the reports, but the State Department said Secretary of State Marco Rubio had spoken on Thursday with Ugandan President Yoweri Museveni. (AP)