A recent plateau in new Covid-19 infections in the United States was likely linked to the "premature" easing of anti-virus efforts, top pandemic advisor Anthony Fauci said Sunday.

While the emergence of coronavirus variants is part of the problem, so are states that are "pulling back on the mitigation" too soon, he told CBS's "Face the Nation."

When case numbers begin to plateau, he said, "you're really in danger of a surge coming up."

"We've seen that in our own country, and that's exactly what's happened in Europe in several of the countries in the European Union, where they plateaued and then started to come back."

President Joe Biden was asked by reporters Sunday for his take on the latest case numbers.

"Based on what I'm hearing that apparently people are letting their guard down, but I'm having a meeting with the team tomorrow and I'll get a better sense," he said.

Crowds in Florida, one of the American states with less restrictive coronavirus curbs
Crowds in Florida, one of the American states with less restrictive coronavirus curbs GETTY IMAGES NORTH AMERICA / JOE RAEDLE

After a spike over the fall and winter in the United States that reached into the hundreds of thousands of new cases daily, infections have come to levels near 50,000 reported per day.

The United States has suffered the highest reported absolute toll at just over 549,000 deaths since the pandemic started, but has now made an aggressive push to roll out vaccines.

Meantime, France, Belgium and Poland on Saturday tightened curbs as coronavirus cases surged in Europe, with France calling the situation there "critical."

"It really is almost a race between getting people vaccinated and having this peak that... we don't want to see," Fauci said.

US states including Texas, Maryland, Connecticut and Mississippi have eased Covid-related restrictions, lifting mask mandates or allowing restaurants, retailers and others to reopen with fewer or no restrictions.

Fauci also warned that travel over the coming Easter holiday could fuel a new surge, as occurred after the year-end holidays.

"Even if on the planes people are wearing masks, when you get to the airport, the check-in lines, the food lines for restaurants, the boarding... invariably increase the risk of getting infected," he said.