President Donald Trump's administration asked a US appeals court on Tuesday to rule a federal judge was wrong to suspend a temporary travel ban imposed on people from seven Muslim-majority countries and all refugees.
The hearing before the San Francisco-based 9th Circuit Court of Appeals judges was the greatest legal challenge yet to the ban enforced by Trump on January 27.
"Congress has expressly authorised the president to suspend entry of categories of aliens," attorney August Flentje, special counsel for the US Justice Department, said under intense questioning from a three-judge panel.
He said the president's executive order was valid under the US Constitution.
Rachel Silverman speaks to TRT World from the US.
The court said at the end of the session that it would issue a ruling as soon as possible. It would likely rule later this week.
The appeals court is only looking at the question of whether the federal judge had the grounds to halt Trump's order.
The Seattle judge, responding to a challenge by Washington state, suspended the order last Friday.
Since then some people from the seven countries who were stuck at airports have made it to the US.
The matter is ultimately likely to go to the US Supreme Court.
Trump's order barred travellers from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen from entering for 90 days and all refugees for 120 days, except refugees from Syria, whom he would ban indefinitely.
Trump, who took office on January 20, has defended the measure, the most divisive act of his young presidency, as necessary for national security.
Individuals, states and civil rights groups challenging the ban said Trump's administration had offered no evidence that the people from Muslim-majority countries posed a threat.
Opponents also assailed the ban as discriminatory against Muslims.
The states of Minnesota and Washington brought the case against the Trump administration.
The judges – two Democratic appointees and one Republican – asked the US government attorney what evidence the executive order had used to connect the seven countries affected by the order with terrorism in the United States.
But Flentje couldn't give any specific examples.
The judges pummelled both sides with questions.
Judge Richard Clifton pushed for evidence that the ban discriminated against Muslims and said he was hearing more allegations than evidence.
"I don't think allegations cut it at this stage," said Clifton, an appointee of former President George W. Bush, a Republican like Trump.
Trump frequently promised during his 2016 election campaign to curb illegal immigration, especially from Mexico, and to crack down on suspected terrorists. His travel ban sparked protests and chaos at US and overseas airports.
National security veterans, major US technology companies and law enforcement officials from more than a dozen states backed a legal effort against the ban.
"I actually can't believe that we're having to fight to protect the security, in a court system, to protect the security of our nation," Trump said at an event with sheriffs at the White House on Tuesday.