A US judge on Saturday granted an emergency stay against US President Donald Trump's order banning refugees and citizens from seven Muslim-majority countries from entering the country.
The temporary ruling by a court in New York means those already in the country or in transit - and who have a valid visa - can remain.
Judge Ann M Donnelly said that without a stay there was an "imminent danger" of "substantial and irreparable injury to refugees, visa-holders and other individuals from nations" subject to Friday's order.
"Our courts today worked as they should as bulwarks against government abuse or unconstitutional policies and orders," said Anthony D Romero, director of the American Civil Liberties Union (ACLU), which brought the case.
"On week one, Donald Trump suffered his first loss in court," he added in a statement.
The ACLU, which posted the judge's order online, had filed its case early Saturday on behalf of two Iraqi men who had been detained at John F Kennedy Airport in New York.
The stay is temporary and another court will have to decide whether to make it permanent.
The judge's ruling came amid reports of refugees and those with valid visas being detained at airports around the US and of other travellers being prevented from boarding flights to the US.
According to CNN, protesters gathered at at least eight major US airports including JFK Airport, Washington Dulles International Airport and Portland International Airport, with further protests scheduled for Sunday.
Hillary Clinton, Trump's Democratic rival in November's presidential election, tweeted her support for the protesters, saying, "I stand with the people gathered across the country tonight defending our values & our Constitution. This is not who we are."
Earlier, Trump insisted his order, which suspends the US refugee admissions programme for four months, blocks Syrian refugees indefinitely and bars entry to all travellers from the seven countries for 90 days, was "not a Muslim ban."
"It's not a Muslim ban. We were totally prepared. It's working out very nicely," Trump told reporters during a photo opportunity at the White House in remarks quoted by CNN.
"You see it at the airports. You see it all over. It's working out very nicely and we're going to have a very, very strict ban, and we're going to have extreme vetting, which we should have had in this country for many years," Trump said.
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