Vowing to protect the country from "foreign terrorists," Trump on January 27 ordered the suspension of all immigration from seven predominantly Muslim countries for 90 days until a rigorous new "extreme vetting" process is put in place.
The White House said the countries targeted are Syria, Iran, Iraq, Libya, Somalia, Sudan, and Yemen. The ban does not apply to non-Muslims from those countries.
A U.S. Homeland Security spokesman said on January 28 that the temporary ban applied to citizens of the seven targeted countries even if they are U.S. green-card holders -- that is, Muslims working toward becoming naturalized U.S. citizens who effectively hold permanent U.S. residency papers.
The order had immediate impact on civilian passenger flights to the United States, with the Dutch airline KLM announcing that it refused to allow onto its flights to the United States seven passengers who were from the targeted countries.
A spokeswoman for KLM, part of the Franco-Dutch Air France KLM group, declined to specify which countries the passengers were from or where they were flying from.
Spokeswoman Manel Vrijenhoek said KLM "had to inform" the seven passengers that "there was no point in us taking them to the United States," adding that there is "still some lack of clarity about whom this ban affects."
In Cairo, seven other passengers were prevented from boarding an EgyptAir flight to New York. Six were from Iraq and one was from Yemen.
Ali Abdi, an Iranian citizen with permanent residency in the United States, told Britain's The Guardian newspaper that Trump's executive order had left him stuck in limbo in Dubai, United Arab Emirates.
Abdi, a doctoral student of anthropology in the United States, said he left New York on January 22 to carry out ethnographic research in Afghanistan.
But he said Trump's order left it unclear whether the Afghan Consulate in Dubai will issue the entry visa he needs to do his field work there.
He said he couldn't go to Iran because he has been outspoken about Tehran's human rights violations, he can't return to the United States, and he cannot stay longer in Dubai because his visa there will soon run out.
Trump also decreed a four-month suspension of the U.S. refugee program for countries other than Syria -- an order affecting refugees from Iraq, Afghanistan, and Pakistan. And he cut in half to 50,000 the number of refugees the United States will accept from around the world during 2017.
A major exception to the refugee bans was for Syrian Christians, who Trump said were persecuted in their homeland.
"I'm establishing new vetting measures to keep radical Islamic terrorists out of the United States of America. Don't want them here," Trump said as he unveiled the orders at the Pentagon.
"We only want to admit those into our country who will support our country and love deeply our people."
Civil rights groups condemned the measures as discriminatory and unconstitutional for targeting a specific religion.
They said the moves, which Trump had promised during his campaign, would strand refugees in dangerous places and backfire by feeding hatred toward the United States in the Muslim world and tarnishing its reputation as a land welcoming of immigrants and the world's "poor and huddled masses."
"'Extreme vetting' is just a euphemism for discriminating against Muslims," said Anthony Romero, executive director of the American Civil Liberties Union.
Ahmed Rehab of the Council on American-Islamic Relations said his group would fight the orders "tooth and nail" in court.
"It is targeting people based on their faith and national origin, and not on their character or their criminality," he told AFP.
Immigration attorneys said the orders were having an immediate chaotic impact on people planning to visit the United States or arranging for relatives in one of the targeted countries to join them in America.
Democrats condemned the move as un-American, saying it would damage the reputation of the United States.
"Today's executive order from President Trump is more about extreme xenophobia than extreme vetting," Democratic Senator Edward Markey said in a statement.
Some Republicans praised the decision, including Representative Bob Goodlatte, chairman of the House of Representatives' Judiciary Committee, who said the extremist group Islamic State had threatened to use the U.S. immigration system.
"I am pleased that President Trump is using the tools granted to him by Congress and the power granted by the constitution to help keep America safe and ensure we know who is entering the United States," Goodlatte said in a statement.
Even before Trump's announcement, prominent people from the targeted regions said they would boycott travel to the United States in protest. An Iranian actress in a film nominated for an Academy Award this year said she would boycott the Los Angeles awards ceremony.
An Iraqi-Kurdish filmmaker, Hussein Hassan, also scrapped plans to attend the U.S. premiere of his critically acclaimed film on Iraq's embattled Yazidi minority, The Dark Wind, scheduled for March.
James Zogby, president of the Arab American Institute, told AP that the orders are "wrongheaded and dangerous in terms of the Middle East."
Iranian-Americans point out that not a single terrorist incident in the United States has involved Iranians, while many of the hijackers involved in the September 11, 2001, attacks in New York and Washington were from Saudi Arabia, which is not on the list of targeted countries.
Moreover, Iran, like the United States and Iraq, has sent troops to battle Islamic State (IS) militants in Iraq and Syria, the group that has inspired the most recent attacks by its followers in the United States.
In Tehran, the government said it would respond to Trump's order by issuing a similar ban that prevents U.S. citizens from entering Iran.
France, Germany, and other U.S. allies also expressed concern about Trump's decision to limit immigration and refugees from some Muslim countries.
French President Francois Hollande said on January 28 that Trump's administration was encouraging "populism and even extremism."
Hollande told other Southern European leaders who were meeting in Lisbon that they must "stand together in Europe" to face an increasingly uncertain world, saying that "what is at stake is populism" and that "the kind of discourse now coming from the United States encourages populism and even extremism."
In Ankara, Turkey's Prime Minister Binali Yildirim said the refugee crisis was a "global issue" and that all countries must do their part to solve the problem.
Abbas al-Bayati, an Iraqi member of parliament, said the curbs were sending the wrong message to Iraqis at a time when Washington is counting on Iraqi forces to battle IS militants in their stronghold of Mosul.
Fellow Iraqi lawmaker Majid Chenkali was less diplomatic, saying Iraq should respond in kind and not allow Americans into Iraq.
"It should be an eye for an eye," he told AP.