US President Joe Biden on Wednesday said decisions to end the required wearing of masks, such as those made by the governors of Texas and Mississippi, amounted to "Neanderthal thinking" given the increasing death toll from the coronavirus pandemic.
Asked if he had a message for Texas and Mississippi, Mr Biden said: "I think it's a big mistake. Look, I hope everybody's realised by now, these masks make a difference."
Mr Biden said the increasing availability of vaccines was making a difference in containing the spread of Covid-19, but it was critical to remain vigilant about wearing masks, washing hands and maintaining social distance.
"The last thing we need is Neanderthal thinking that, 'in the meantime, everything's fine, take off your mask, forget it'. It still matters," Mr Biden said before a meeting with Republican and Democratic politicians.
He said more than 511,000 people had died of Covid-19 in the US and it would take time before everyone eligible was vaccinated against the disease.
Daily cases in the US remain above 50,000, even after the distribution of more than 100 million vaccine doses to 50 million people, according to federal data.
"It is critical that they follow the science: Wash your hands, hot water, do it frequently. Wear a mask and stay socially distanced. I know you know that. I wish the heck some of our elected officials would," Mr Biden said.
Texas Governor Greg Abbott ordered the most sweeping relaxation of coronavirus restrictions of any US state on Tuesday, lifting a mask mandate and saying most businesses can open at full capacity next week.
Mississippi Governor Tate Reeves on Tuesday also lifted a mask mandates across his state and removed restrictions on business operations.
White House senior adviser Andy Slavitt said the federal government planned to spend $100 million to help bring about the partnership announced on Tuesday between pharmaceutical companies Merck and Johnson & Johnson to accelerate vaccine production.
The infusion will help Johnson & Johnson increase the production of its one-shot vaccine, Mr Slavitt said.
Johnson & Johnson was contracted to deliver 200 million doses to the federal government by the end of May and about a billion doses globally by the end of 2021.
"Over time we believe Merck will be able to double the capacity of Johnson & Johnson," Mr Slavitt said.
Mr Biden said on Tuesday that the US would have enough vaccine supplies to inoculate all adults by May.
Johnson & Johnson, Pfizer and Moderna agreed to deliver 700 million doses by the middle of the year between them.