The U.S. State Department on Monday advised its citizens not to visit Japan due to a surge in coronavirus cases, raising its travel alert to the highest level of 4 just two months before the start of the Tokyo Olympics.

Although the U.S. Olympic and Paralympic Committee played down concerns that the alert would affect the participation of American athletes in the Summer Games, the latest development could raise further safety questions about whether the global sporting event should go ahead amid the ongoing pandemic.

"We feel confident that the current mitigation practices in place for athletes and staff...coupled with the testing before travel, on arrival in Japan, and during games time, will allow for safe participation of Team USA athletes this summer," the committee said in a statement.

Japan has already decided not to allow overseas spectators and volunteers to enter the country for the games, scheduled to be staged from July 23.

"I have heard from the U.S. government that the decision and the dispatch of U.S. athletes are not related," Japanese Foreign Minister Toshimitsu Motegi told a parliamentary committee in Tokyo.

"Travel (from the United States to Japan) is not banned when it is necessary," he said. "I know that there is no change whatsoever in the U.S. position that it will support the Japanese government's decision to realize the Olympics and Paralympics."

The State Department said the upgrade of its advisory by one level reflected the travel health notice by the U.S. Centers for Disease Control and Prevention, which has labeled Japan as facing a "very high level of COVID-19."

"Because of the current situation in Japan, even fully vaccinated travelers may be at risk for getting and spreading COVID-19 variants and should avoid all travel to Japan," the CDC said.

The CDC's "very high level of COVID-19" warning, or level 4 notice, is issued when the coronavirus incidence rate -- defined as cumulative new cases over the past 28 days per 100,000 population -- hits more than 100.

Japan met the level 4 criteria on Friday and its current incidence rate is 120 cases per 100,000, an official of the U.S. health protection agency said.

Japan has recently been grappling with another wave of infections, with sources saying the government is considering extending the coronavirus state of emergency covering Tokyo, Osaka and other areas beyond the current expiration date of May 31.

But the Japanese government has been emphasizing that the games can still be held safely, saying it will ensure proper anti-virus measures are in place for athletes and staff to participate.

John Coates, an International Olympic Committee vice president, said Friday the Tokyo Olympics can be held as planned even if the Japanese capital is under a state of emergency.

U.S. President Joe Biden expressed support for Japanese Prime Minister Yoshihide Suga's "efforts to hold a safe and secure Olympic and Paralympic Games this summer" when the two met in mid-April, according to a joint statement released after their talks.

In March last year, the State Department issued an advisory for Americans to avoid all international travel amid the worldwide outbreak of the virus.

The global advisory was lifted in August, and the country-specific guidance for travel to Japan had since remained at level 3, under which U.S. citizens are urged to "reconsider travel" to the destination.

Around 150 countries are currently subject to the department's level 4 "do not travel" warning.

In Japan, more than 722,000 confirmed cases of COVID-19 with around 12,350 deaths have been reported, according to a tally by Johns Hopkins University.

The United States remains the country worst hit by the pandemic, with the number of infections totaling more than 33 million and deaths exceeding 590,000. But its situation has been improving amid a massive vaccine rollout.