US immigration officials on Monday deported an Iranian student headed to a Boston university despite efforts by the American Civil Liberties Union (ACLU) and other advocates to block the removal.

The deportation of Mohammad Shahab Dehghani Hossein Abadi, a 24-year-old Iranian citizen enrolled at Northeastern University, comes after US Customs and Border Protection (CBP) announced an "enhanced security posture" amid heightened tensions with Iran.

The case had raised new questions about the fair treatment of Iranians by immigration authorities under the administration of US President Donald Trump. Massachusetts Senator Elizabeth Warren, a leading Democratic presidential candidate, called on CBP to halt Abadi's deportation on Monday night and pledged to fight Trump's "xenophobic policies".

Boston-based lawyer Kerry Doyle, who took on the case along with lawyers from two other private firms and the ACLU, said Abadi shared immigration paperwork electronically that showed he had been denied entry due to a concern that he would remain in the United States beyond the scope of his student visa.

An official with the Department of Homeland Security said that charge was a "catch all" reason used to deny entrants. The official, who requested anonymity to discuss the case, said border authorities were concerned that Abadi had immediate family members with business ties to Hezbollah, which is considered a terrorist organisation by the US.

Doyle rejected that allegation and said a summary of Abadi's interview with border authorities suggested confusion over his father's identity.

"It appeared that there was someone with a similar name or there was some mix-up," she said.

Boston-based US District Judge Allison Burroughs halted Abadi's removal on Monday for 48 hours after an emergency petition filed by the ACLU. The DHS official said Abadi already had boarded a flight to leave the US at that point.

Carol Rose, executive director at the ACLU of Massachusetts, argued in a statement on Tuesday that border authorities could have stopped the removal, but "defied a federal court order and deported Shahab without due process".

Whether CBP officials could have retrieved Abadi from the flight on Monday evening remained unclear.

A second Boston-based federal judge, US District Judge Richard Stearns, said during a hearing on Tuesday that the challenge to Abadi's detention was moot since he had been removed from the country, according to the ACLU and the DHS official.

Visa cancelled

Abadi was granted a US student visa approximately one week ago, but had that visa cancelled following his arrival at Boston Logan International Airport on Sunday, according to court documents.

Following the January 3 US military strike in Iraq that killed the top Iranian general, Qassem Soleimani, dozens of Iranian Americans with US citizenship or permanent residency were detained by US immigration officials at a border crossing in Washington state.

Local advocacy organisations criticised the detentions - which they said stretched to 12 hours - as unusual and troubling.

CBP said in a January 10 statement that it was operating with an "enhanced security posture" amid tensions with Iran. That came after retaliatory Iranian attacks on bases housing US forces.

The ACLU of Massachusetts said at least 10 Iranian students had been denied entry at US airports since August 2019, with seven of those denials occurring at Logan International Airport.