The Centers for Disease Control and Prevention and the State Department on Monday said to avoid travel to the U.K. as the delta variant of Covid-19 continues to spread.

The warnings are “Level 4,” the CDC and State Department’s highest. While not binding, they come after airline executives and other members of the travel industry have pressed the Biden administration to loosen existing Covid travel restrictions that have devastated demand for international bookings.

The United States has had an entry ban in place for non-U.S. citizens from the EU, U.K. and other countries for much of the coronavirus pandemic, though several European nations have recently opened their doors to international visitors. Canada, however, said Monday it will allow fully vaccinated U.S. citizens into the country for nonessential travel starting Aug. 9.

The White House and the British Embassy in Washington didn’t immediately respond to a request for comment.

The CDC said if individuals must travel to the U.K., they should be fully vaccinated against Covid. Meanwhile, England lifted remaining Covid-19 restrictions on Monday, allowing for indoor gatherings and the reopening of nightclubs.

But Covid infections remain high across the U.K. with 316,691 cases reported over the last seven days, up by about 43% from the previous seven-day period, according to a CNBC analysis of data compiled by Johns Hopkins University.

U.S. airline stocks fell sharply on Monday as an increasing number of Covid cases raised concerns about the economic recovery and the potential impact on the recent resurgence in travel demand after a slump for much of the past year.

Covid cases in the U.S. have jumped by about 66% in the past week to a seven-day average of about 32,300 new cases per day, according to Johns Hopkins data.

— CNBC’s Holly Ellyatt contributed to this article.