The fall-out from President Donald Trump's immigration crackdown widened as residents and visa-holders from seven Muslim-majority countries who had left the United States found they could not return for 90 days.
It was a period of limbo for an unknown number of non-American citizens from Iraq, Syria, Iran, Sudan, Libya, Somalia or Yemen now barred from the country where they were studying or had lived, perhaps for years.
A federal law enforcement official who confirmed the temporary ban said there was an exemption for foreigners whose entry is in the US national interest. It was not immediately clear how that exemption might be applied.
Mr Trump's order exempts diplomats and t hose already in the US with a visa or green card will be allowed to stay.
Airlines were being notified by Customs and Border Protection about passengers they needed to prevent from flying.
Mr Trump's order barred all refugees from entering the US for four months, and indefinitely halted any from Syria. He said the ban was needed to keep out "radical Islamic terrorists".
The next group of refugees was due to arrive in the US on Monday, but the official said they would not be allowed into the country.
The president's order immediately suspended a programme that last year resettled in the US about 85,000 people displaced by war, political oppression, hunger and religious prejudice.
Mr Trump indefinitely blocked those fleeing Syria, where a civil war has raged, and imposed a 90-day ban on all immigration to the US from the seven Muslim majority nations.
"We want to ensure that we are not admitting into our country the very threats our soldiers are fighting overseas," he said as he signed the order at the Pentagon. "We only want to admit those into our country who will support our country and love deeply our people."
Mr Trump said the halt in the refugee programme was necessary to give agencies time to develop a stricter screening system.
While the order did not spell out what additional steps he wants the departments of Homeland Security and State to take, the president directed officials to review the refugee application and approval process and find any more measures that could prevent those who pose a threat from using the refugee programme.
The US may admit refugees on a case-by-case basis during the freeze, and the government will continue to process requests from people claiming religious persecution, "provided that the religion of the individual is a minority religion in the individual's country".
In an interview with CBN News, Mr Trump said persecuted Christians would be given priority in applying for refugee status.
"We are going to help them," Mr Trump said. "They've been horribly treated."
The order was signed on Mr Trump's most robust day of national security and foreign policy at the start of his presidency.
As a candidate, Mr Trump called for a temporary ban on all Muslim immigration to the US. He later shifted his focus to putting in place "extreme vetting" procedures to screen people coming to the US from countries with terrorism ties.
The State Department said the three-month ban in the directive applied to Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen - all Muslim-majority nations.
The Council on American-Islamic Relations said it would challenge the constitutionality of the executive order.
"There is no evidence that refugees - the most thoroughly vetted of all people entering our nation - are a threat to national security," said Lena Masri, the group's national litigation director. "This is an order that is based on bigotry, not reality."
During the past budget year, the US accepted 84,995 refugees, including 12,587 people from Syria. President Barack Obama had set the refugee limit for this budget year at 110,000.
According to Mr Trump's executive order, he plans to cut that to 50,000.
The International Rescue Committee called the suspension of the refugee resettlement programme a "harmful and hasty" decision.
IRC President David Miliband said: "America must remain true to its core values. America must remain a beacon of hope."
Mr Miliband praised the United States' record as a resettlement destination and said: "This is no time for America to turn its back on people ready to become patriotic Americans."
The head of a leading refugee aid agency said the ban hurts innocents fleeing violence.
Jan Egeland, of the Norwegian Refugee Council, said the decision "will not make America safer, it will make America smaller and meaner".
He said the decision dealt a "mortal blow" to the idea of international responsibility for those fleeing persecution.
The US is leading a "race to the bottom" in which politicians in wealth countries provide "zero moral leadership", he said.
Malala Yousafzai, shot in the head by the Pakistani Taliban in 2012 to stop her campaigning for girls' education and co-winner of the 2014 Nobel peace prize, said she is heart-broken by the ban.
Ms Yousafzai implored Mr Trump "not to turn his back on the world's most defenceless children and families".
Refugees and immigrants, she said, have "helped build your country".
Iran's foreign ministry announced it will limit issuing visas to American tourists in retaliation against the immigration crackdown.
The official IRNA news agency carried a statement by the Iranian foreign ministry saying Iran will resort to "counteraction" to Mr Trump's executive order.
The statement said: "Iran, to defend the dignity of the great Iranian nation, will implement the principle of reciprocity until the removal of the insulting restriction against Iranian nationals."
The statement adds: "It will apply corresponding legal, consular and political actions."
The two countries have had no diplomatic relations since 1979 when militants stormed the US embassy.
Two of the first people blocked from entering the United States were Iraqis with links to the US military.
Hameed Khalid Darweesh and Haider Sameer Abdulkhaleq Alshawi were detained by immigration officials after landing at New York's Kennedy airport on Friday night.
Darweesh had worked as an interpreter for the US Army when it invaded Iraq in 2003. Later he worked as a contract engineer.
He was allowed into the US on Saturday afternoon, hours after his lawyer petitioned a federal court to let the two men go.
In their court filing, his lawyers said Alshawai's wife had worked for a US security contractor in Iraq. Members of her family had been killed by insurgents because of their association with the US military.
Later Mr Trump said the crackdown "is not a Muslim ban" and said the measure was "working out very nicely."