President Donald Trump on Monday lifted a ban on travellers from much of Europe and Brazil, effective from January 26, after the US announced all incoming air passengers will need a negative Covid-19 test before boarding.
"This action is the best way to continue protecting Americans from Covid-19 while enabling travel to resume safely," Mr Trump said.
Travel bans remain in place for China and Iran.
The Centres for Disease Control and Prevention announced last Tuesday that all air passengers bound for the US are required to test negative for Covid-19 within three days of their departure.
The test policy will also take effect on January 26, and expands on a previous rule for British travellers.
It came into effect in December, after the emergence of a coronavirus variant in the UK, which was believed to be more transmissible.
The CDC also recommends that travellers are tested again three to five days after their arrival, and stay home for at least seven days.
President-elect Joe Biden's press secretary on Monday quickly dismissed Mr Trump's lifting of the travel ban on Europe and Brazil.
"On the advice of our medical team, the administration does not intend to lift these restrictions," Jen Psaki tweeted.
"In fact, we plan to strengthen public health measures around international travel in order to further mitigate the spread of Covid-19."
Mr Biden will be inaugurated on Wednesday.
Some epidemiologists have warned it is likely that new, more transmissible variants are already established in the US, the hardest-hit country in the world.
As of Monday, the US had recorded more than 24 million cases of Covid-19, with nearly 400,000 deaths.