The U.S. is moving to require that all air travelers entering the country show a negative COVID-19 test performed within one day of departure in response to concerns about a new coronavirus variant, the Centers for Disease Control and Prevention (CDC) said late on Tuesday.

Currently, vaccinated international air travelers can present a negative test result obtained within three days from their point of departure. Nearly all foreign nationals must be vaccinated to enter the United States. Unvaccinated travelers currently must get a negative COVID-19 test within one day of arrival.

The new one-day testing requirement would apply equally to U.S. citizens as well as foreign nationals.

Reuters reported earlier that a draft proposal was circulating among government agencies for the stricter testing requirement.

A CDC spokeswoman confirmed the agency is working to modify its global testing rules for travel "as we learn more about the Omicron variant; a revised order would shorten the timeline for required testing for all international air travelers to one day before departure to the United States."

The administration is also considering whether to require air travelers to get another COVID-19 test within three to five days after arrival in the United States, officials said.

The CDC did not confirm that, but noted it continues to recommend all "travelers should get a COVID-19 viral test 3-5 days after arrival" and "post-travel quarantine for any unvaccinated travelers."

The stricter rules could be announced Thursday, but it was not clear when they might take effect.

CDC Director Rochelle Walensky said the agency "is evaluating how to make international travel as safe as possible, including pre-departure testing closer to the time of flight and considerations around additional post-arrival testing and self-quarantines."

On Monday, the White House barred nearly all foreign nationals who have recently been in South Africa and seven other southern African countries over concerns about the Omicron variant.

A White House official said earlier Tuesday the administration is evaluating COVID-19 measures "including considering more stringent testing requirements for international travel."

On Tuesday, the CDC advised Americans against travel to Niger, Papua New Guinea, Poland, and Trinidad and Tobago, citing COVID-19 concerns.

The CDC now lists about 80 foreign destinations as having "Level Four," its highest level of COVID-19 transmission, and discourages Americans from traveling to those destinations.