The US will start to require negative Covid-19 tests from international travellers entering the country, the Centres for Disease Control and Prevention said.
Travellers must be tested for the coronavirus at some point in the three days before their US-bound flight.
They are asked to provide proof of the negative results or medical documents saying they have recovered from Covid-19 before boarding.
The order was signed by CDC director Robert Redfield on Tuesday and will go into effect from January 26.
"Testing does not eliminate all risk," Mr Redfield said.
"But when combined with a period of staying at home and everyday precautions like wearing masks and social distancing, it can make travel safer, healthier and more responsible by reducing spread on planes, in airports and at destinations.”
The CDC order also recommends that travellers stay home for seven days after their return and take a test within three to five days.
The CDC gave new variants around the world as one reason behind the new requirement.
"Variants ... continue to emerge in countries around the world, and there is evidence of increased transmissibility of some of these variants," the CDC said.
"With the US already in surge status, the testing requirement for air passengers will help slow the spread of the virus as we work to vaccinate the American public."
The health agency said the order added to one released in December that required negative tests for travel between the US and the UK after news of the variant spreading.
The British variant of Covid-19 was first discovered in Colorado and California, among other states, signalling an undetected and uncontrolled spread of the variant despite travel test requirements.
