WASHINGTON

US President Donald Trump announced Wednesday evening a ban that is set to prohibit travel to the US from a dozen countries and restrict travel from seven others over alleged security risks.

Trump issued the directive in a presidential proclamation and an accompanying video message in which he said a recent attack on a Boulder, Colorado march for Israeli hostages in Gaza "has underscored the extreme dangers posed to our country by the entry of foreign nationals who are not properly vetted, as well as those who come here as temporary visitors and overstay their visas."

"Very simply, we cannot have open migration from any country where we cannot safely and reliably vet and screen those who seek to enter the United States," he said in the video. "The strength of the restrictions we're applying depends on the severity of the threat posed. The list is subject to revision based on whether material improvements are made, and likewise, new countries can be added as threats emerge around the world, but we will not allow people to enter our country who wish to do us harm and nothing will stop us from keeping America safe."

The White House said in a statement that Trump took the action after reviewing a report from Secretary of State Marco Rubio and other officials

It said the restrictions are being imposed because countries either had inadequate screening and vetting processes, which hinder "America’s ability to identify potential security threats before entry," or their nationals have high rates of overstaying their visas, while other nations "lack cooperation in sharing identity and threat information, undermining effective U.S. immigration vetting."

Trump's order specifically prohibits people from Afghanistan, Myanmar, Chad, the Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan and Yemen from entering the US. An additional seven countries -- Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela -- will face partial restrictions and limited entry of their nationals.

The ban and restrictions are set to take effect at 12.01 am Eastern Time on Monday.