As US President Donald Trump’s order targeting citizens from seven predominantly Muslim countries reverberated across the world on Saturday, it became increasingly clear that the controversial measure he had promised during his presidential campaign was casting a wider net than even his opponents had feared.

Confusion and concern among immigrant mounted throughout Saturday as travelers from the Middle East were detained at US airports or sent home.

Trump’s policy of barring citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen has caused outrage around the world.

The Republican billionaire signed an executive order on Friday that suspended travel visas for anyone from those seven “countries of particular concern” from entering the US for at least 90 days.

But as the day progressed, administration officials confirmed that the sweeping order also targeted US legal residents from the named countries — green-card holders — who happened to be abroad when it was signed. Also subject to being barred entry into the United States are dual nationals, or people born in one of the seven countries who hold passports even from US allies such as the United Kingdom.

Within hours of President Trump’s executive order limiting immigration from Muslim countries, green card and visa holders were already being blocked from getting on flights to the US.

The Arab-American Anti-Discrimination Committee said people who had already landed were being sequestered at airports and told they have to return to their point of origin.

The Department of Homeland Security issued a directive at 4:30 p.m on Saturday ordering the Customs and Border Protection to enforce the executive order.

“For those already here, we won’t actually know until the flights back to these areas begin departing,” Abed Ayoub of the ADC said about the crisis.

“We’re hearing from a lot of people concerned about family members, friends, classmates. We’re hearing about a lot of folks asking ‘should I cancel my plans,’ and from folks who had to cancel events because of this.”

Customs officials said the number of people who arrived here and were turned back was not immediately available Friday night.

“It takes time to collect all the numbers,” a spokesman said.

“It will be a decision from the highest levels of The Department of Homeland Security to decide if and when the data may be available.”

Iran in a swift reaction invoked the principle of reciprocity by blocking American citizens from entering the country in “retaliation” for Trump’s ban on travellers from the seven majority-Muslim countries.

Tehran’s foreign ministry said in a statement it would enforce its own ban “until the offensive US limitations against Iranian nationals are lifted”.