There are no U.S. cases of the new omicron Covid variant, the CDC said late Friday, referring to a heavily mutated strain of the virus that has been classified as a “variant of concern” by the World Health Organization.

“No cases of this variant have been identified in the U.S. to date,” according to the statement by the Centers for Disease Control and Prevention.

“CDC is continuously monitoring variants and the U.S. variant surveillance system has reliably detected new variants in this country. We expect Omicron to be identified quickly, if it emerges in the U.S.,” it said.

The newly identified strain — referred to as lineage B.1.1.529 — was first detected in South Africa and raised concerns due to the rapid rise in the number of coronavirus cases in the country’s Gauteng province.

The UN health agency only designates Covid strains as variants of concern when they’re more transmissible, more virulent or more adept at evading vaccines and therapeutics.

“This variant has a large number of mutations, some of which are concerning,” the World Health Organization said. “Preliminary evidence suggests an increased risk of reinfection with this variant, as compared to other [variants of concern]. The number of cases of this variant appears to be increasing in almost all provinces in South Africa.”

The U.S. on Friday imposed travel restrictions for non-U.S. citizens from South Africa and seven other countries. The restrictions will begin from Monday, and are part of a global effort to blunt the spread of omicron, according to senior Biden administration officials.

The other countries included in the ban were Botswana, Eswatini, Lesotho, Malawi, Mozambique, Namibia and Zimbabwe.

There was no indication of how long the restrictions will be in place.

— CNBC’s Christina Wilkie contributed to this report.