The U.S. government has expanded a sweeping pause on legal immigration applications to include those filed by people from an additional 20 countries that President Trump added to his "travel ban" proclamation this week, a U.S. official with direct knowledge told CBS News on Thursday.

The move, which mainly affects immigrants who hail from certain African and Asian countries, further escalates a wide-ranging crackdown on legal immigration expanded by the Trump administration this month. Many of those affected by the pause are likely to be legal immigrants who are currently in the U.S. and are seeking to change their status or become citizens.

Earlier in December, the Trump administration directed U.S. Citizenship and Immigration Services to completely freeze all immigration petitions - including requests for American citizenship and permanent residency - made by those already in the U.S. who are nationals of the 19 countries he banned or restricted travel from in June. That order is colloquially known as the "travel ban."

It was one of several immigration restrictions the administration announced in the wake of the Thanksgiving week shooting of two National Guard soldiers in Washington, D.C., an attack allegedly carried out by an Afghan national. The administration also suspended all decisions for asylum cases handled by USCIS and the processing of all immigration and visa requests by Afghans.

Earlier this week, Mr. Trump expanded that "travel ban" proclamation to include 20 additional nations, fully barring immigrants and travelers from 5 new countries and partially restricting the entry of people from another 15 nations.

A U.S. official who requested anonymity to discuss internal changes that have not been formally announced told CBS News on Thursday that USCIS has expanded its suspension of immigration cases to include the new nationalities added to Mr. Trump`s proclamation on Tuesday.

The pause will now affect nationals of Burkina Faso, Mali, Niger, South Sudan and Syria, the new countries facing full travel bans. It will also impact those hailing from Angola, Antigua and Barbuda, Benin, Cote d`Ivoire, Dominica, Gabon, Gambia, Malawi, Mauritania, Nigeria, Senegal, Tanzania, Tonga, Zambia and Zimbabwe. The last set of countries face partial restrictions under the latest proclamation.

Previously, the suspension of immigration cases applied to nationals of Afghanistan, Burundi, Chad, Cuba, the Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Laos, Myanmar, Sierra Leone, Somalia, Sudan, Togo, Turkmenistan, Yemen and Venezuela. In his latest proclamation, Mr. Trump imposed a full entry ban on citizens of Laos and Sierra Leone, which previously faced partial restrictions.

In a statement posed on social media late Thursday, USCIS Director Joseph Edlow appeared to reference the expansion.

"USCIS is conducting a comprehensive review of anyone from anywhere who poses a threat to the U.S., including those identified in the President`s latest proclamation to restore law and order in our nation`s immigration system," Edlow wrote.

Taken together, Mr. Trump`s latest "travel ban" decree affects nationals of over 60% of the countries in Africa and roughly 20% of all nations across the globe.

Mr. Trump has argued the broad restrictions are designed to safeguard national security and address concerns about the ability to vet people from the affected nations. But critics of his administration have denounced the policy as discriminatory, since it mainly applies to nations in Africa and Asia.