A sweeping new travel ban on citizens from a dozen nations was announced by the White House on Wednesday, reviving a defining effort from the first Trump administration to crack down on entries from specific countries.

Donald Trump has signed a ban on travel to the US from 12 countries citing national security risks, according to the White House. The US president said the list could be revised if "material improvements" were made and additional countries could also be added as "threats emerge around the world".