Donald Trump has said that judges who blocked his migration ban relating to 7 mostly Muslim countries are putting the US in peril.
The US President said he has instructed border officials to check people entering the country “very carefully.”
On Friday, federal judge James Robart halted the order that temporarily blocked all refugees and citizens of seven Muslim-majority countries from entering the US.
The 9th US Circuit Court of Appeals on Sunday denied a formal request by the US Department of Justice to lift the ruling.
The hearing gave the Trump administration until Monday afternoon to file more arguments before a final decision is made - meaning the ban could be up and running again soon.
The government has until 5 p.m. PST on Monday to submit additional legal briefs justifying the executive order.
Following that, the court is expected to act quickly, and a decision either way may ultimately result in the case reaching the U.S. Supreme Court.
On Twitter, Mr Trump said: "I have instructed Homeland Security to check people coming into our country VERY CAREFULLY. The courts are making the job very difficult!
I have instructed Homeland Security to check people coming into our country VERY CAREFULLY. The courts are making the job very difficult!
— Donald J. Trump (@realDonaldTrump) February 5, 2017
"Just cannot believe a judge would put our country in such peril. If something happens blame him and court system. People pouring in. Bad!"
Just cannot believe a judge would put our country in such peril. If something happens blame him and court system. People pouring in. Bad!
— Donald J. Trump (@realDonaldTrump) February 5, 2017
He did not elaborate on what threats the country potentially faced.
The uncertainty has opened a window for travellers from the seven affected countries to enter the United States.
In a personal attack on Judge Robart on Saturday, Mr Trump described him as a "so-called judge" in another series of ill-tempered tweets.
He accused the Seattle judge of opening "up our country to potential terrorists and others that do not have our best interests at heart."
The President's decree, signed on 27 January, barred entry for 120 days of any refugees awaiting resettlement.
Citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen were also banned for 90 days.
President Trump’s critics have said the measures are discriminatory, unhelpful and legally dubious.
Meanwhile, the White House announced on Sunday that Mr Trump will meet NATO leaders in May.
Mr Trump expressed "strong support for NATO" but called on European members to pitch in more, the White House said in a statement.
Additional reporting by IRN ...
