US President Donald Trump signed a new travel ban that comes into effect on Monday targeting 12 countries, including Afghanistan, Iran and Yemen, reviving one of the most controversial measures from his first term.

Trump said on Wednesday the measure was spurred by a makeshift flamethrower attack on a Jewish protest in Colorado that US authorities blamed on a man they said was in the country illegally.

The move bans all travel to the United States by nationals of Afghanistan, Myanmar, Chad, Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan and Yemen, according to the White House.

Trump also imposed a partial ban on travelers from seven other countries: Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela. Some temporary work visas from those countries will be allowed.

"The recent terror attack in Boulder, Colorado, has underscored the extreme dangers posed to our country by the entry of foreign nationals who are not properly vetted," Trump said in a video message from the Oval Office posted on social media platform X.