WASHINGTON, Jan. 25 (NBCNews) - President Joe Biden signed restrictions Monday on travel to the United States to mitigate Covid-19 transmission.

The ban prevents most non-U.S. citizens from entry if they have recently been in South Africa, where a new strain of Covid-19 has been identified. The virus has killed more than 420,000 people and infected upward of 25 million across the U.S., according to an NBC News tracker.

Biden additionally reinstated broader restrictions that were in effect much of the past year but were rescinded by President Donald Trump days before his term ended. The limits affect non-U.S. citizens traveling from the United Kingdom, Ireland and much of Europe in what is known as the Schengen countries, which share a common visa process. Travelers from Brazil would also be affected.

Before Biden took office, incoming White House press secretary Jen Psaki in a tweet criticized Trump's decision to rescind the bans he had implemented.

"With the pandemic worsening, and more contagious variants emerging around the world, this is not the time to be lifting restrictions on international travel," she said.

The restrictions were set to be lifted Tuesday.

The Centers for Disease Control and Prevention said Sunday that, beginning Tuesday, it will no longer consider exceptions to its requirement that international travelers present negative coronavirus tests. Airlines had asked the agency to relax the rule for some countries with limited testing capacity.

"As variants of the SARS-CoV-2 virus continue to emerge in countries around the world, there is growing evidence of increased transmissibility of some of these variants, as well as unknown health and vaccine implications," a CDC spokesman said in a statement. "Testing before and after travel is a critical layer to slow the introduction and spread of COVID-19 and emerging variants."