Even valid Green card and visa holders were being blocked from boarding US-bound flights within hours of Donald Trump issuing an executive order limiting immigration from several Muslim countries, the Independent reported on Saturday.

US airports were also said to have ordered some passengers who had managed to board flights to return to their point of origin, according to the Arab-American Anti-Discrimination Committee (ADC).

ADC’s policy director Abed Ayoub warned visas were being denied with immediate effect and the ban would also apply to green card holders attempting to return to the US overnight.

Trump suspended refugee admissions to the country for 120 days as part of measures he claimed would “keep radical Islamic terrorists out of the US”.

The executive order, titled “Protecting the Nation From Foreign Terrorist Entry Into The United States”, also banned Syrian refugees indefinitely until “significant changes” are made, and halved the annual cap on refugees to 50,000.

The order will affect people from “countries of particular concern”, expected to include Syria, Iraq, Iran, Libya, Somalia, Sudan and Yemen.

The ADC warned against green card holders from the listed countries from travelling outside the US until the ban is lifted.