Judges expressed skepticism over the need for the travel ban, asking whether there was any evidence of a link between the seven countries and terrorism. The court said a decision would come "as soon as possible."
A three-judge panel from the 9th US Circuit Court of Appeals heard arguments from the US government on Tuesday, which sought to get the executive order signed by US President Donald Trump on January 27 reinstated.
"Congress has expressly authorized the president to suspend entry of categories of aliens," attorney August Flentje, special counsel for the US Justice Department, said under intense questioning.
"That's what the president did here," Flentje added at the start of an oral argument that lasted over an hour. He insisted the order was valid under the US Constitution.
Justice Dept vs US states
Also presenting their arguments were several US states that oppose Trump's ban on travelers from seven predominantly Muslim nations.
Unusually, both sides' arguments were heard by phone and broadcast online via the court's website as well as on American news channels.
The order, which blocks citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen for 90 days, is currently on ice after a District judge in Seattle ruled it was illegal - a decision reinforced by a court in San Francisco.
All refugees are also blocked from entering the US for 120 days, except those from Syria, whom Trump said he would ban indefinitely.
Tuesday's hearing ended without a ruling and a court spokesman said it was unlikely that any decision would be made by the end of the day. One of the judges said the ruling would be made "as soon as possible."
Highlighting terror threat
During Tuesday's hearing, judges expressed skepticism over the need for the ban, asking whether there was any evidence of a link between the seven countries and terrorism. Flentje defended Trump's block, citing evidence that Somalis in the US were tied to the al-Shabaab terror group.
But Washington State Solicitor General Noah Purcell told the appeals panel that the order had harmed thousands of state residents by splitting up families, delaying students hoping to travel, and stopping foreign travel by green card holders and their relatives. The court also heard that the ban was discriminatory against Muslims.
Washington, Minnesota and other states have called for the appeals court to allow the temporary halt on the executive order to stand.
There have been protests against the travel ban
Long legal battle likely
The appeals court is not making a decision whether the order is legal, per se, but rather whether it should be put on hold while courts are deciding whether it is legal.
Some experts think that it is likely that the judges will not reinstate Trump's order - though they could also ask him to amend the decree in order to reinstate it. The appeals court had previously rejected a request to immediately reinstate the order.
The party that loses the case is likely to challenge the court's decision - the case could then go to the Supreme Court, the highest judiciary authority in the US.
Ahead of Tuesday's hearing, White House spokesman Sean Spicer said he felt confident that the president's order would ultimately be upheld. "All that's at issue tonight in the hearing is an interim decision on whether the president's order is enforced or not until the case is heard on the actual merits of the order," he told reporters.
But those opposed to Trump's order have argued that it violates the US Constitution because it goes against fundamental principles including those on equality, freedom of movement and freedom of religion. Critics have said that the order is also a case of presidential overreach.