Postponement of the Tokyo Olympics appeared increasingly inevitable Monday as a growing number of countries signaled their athletes would not participate if the Games were held as scheduled this summer, the United States advocated for a delay and Japanese officials conceded for the first time that one was possible.

A whirlwind 24-hour period started Sunday with International Olympic Committee President Thomas Bach issuing a letter to Olympic athletes, saying the IOC was considering delaying the Summer Games because of the novel coronavirus pandemic. Since 1896, the Summer Olympics have taken place every four years except for 1916, 1940 and 1944, when they were canceled because of world wars. Bach said a cancellation had been ruled out and that the IOC would consider different scenarios and make a final decision within the next four weeks.

That long timetable led Canada to call for a postponement Sunday night and say it would not send any athletes to Tokyo if the Games began as scheduled July 24. Australia and Germany followed with similar announcements Monday, and other countries, such as the United States, Britain, Brazil, ­Norway and Slovenia, either urged a postponement or said conditions must improve if they're to participate.

On Monday night, the United States' Olympic governing body issued its strongest statement to date, a gentle vote for postponement. In a joint statement, U.S. Olympic and Paralympic Committee chair Susanne Lyons and USOPC CEO Sarah Hirshland said that after polling 1,780 athletes, the USOPC had reached the conclusion that postponement was the best option.

The USOPC said 68 percent of the athletes it surveyed did not think the Games could be fairly competed this summer, and 65 percent said their training has been severely impacted by the coronavirus pandemic.

"Even if the current significant health concerns could be alleviated by late summer, the enormous disruptions to the training environment, doping controls and qualification process can't be overcome in a satisfactory manner," Lyons and Hirshland said in the statement. "To that end, it's more clear than ever that the path toward postponement is the most promising, and we encourage the IOC to take all needed steps to ensure the Games can be conducted under safe and fair conditions for all competitors."

Earlier Monday, Dick Pound, the longest-serving IOC board member, told USA Today that "postponement has been decided," but the IOC has given no indication that a delay was certain. In a request to comment on Pound's assertion, an IOC spokesman said, "It is the right of every IOC Member to interpret the decision of the IOC [executive board] which was ­announced yesterday."

Pound is one of 100 IOC members, having joined the committee in 1978. He is not one of the 15 members of the IOC's powerful executive board, which plays a pivotal role in all important Olympic matters.

Aruban IOC executive board member Nicole Hoevertsz said in an email Monday afternoon that the board "discussed and took a decision about" postponement Sunday, signaling the IOC had not changed its stance. She then pointed to the portion of the IOC's official statement that said it would start discussions about postponement scenarios and was confident those discussions would be completed within four weeks. A postponement of any length would involve many complexities, with global and local ramifications on athletes and residents, sponsors and television networks.

"You're looking at a postponement," Pound said. "I think that's out there now. . . . We're all reading the tea leaves and so on, but the Japanese themselves are talking about postponing. A lot of national Olympic committees and countries are calling for a postponement."

Until Monday, Japan had insisted that the Games must go ahead as scheduled, although Prime Minister Shinzo Abe said last week that the priority must be to hold the Olympics in a “complete manner.” On Monday, he told parliament this might mean the dates would have to change.

“If that is difficult, we would have no choice but to decide to postpone, with athletes as the first priority,” Abe said, underlining that an outright cancellation is not an option.

Later Monday, Tokyo 2020 Organizing Committee President Yoshiro Mori acknowledged it was time to consider alternatives.

“What we are going to do before anything else is to start by simulating about whether we postpone one month, three months, five months, one year,” Mori said. “We need to make a simulation about the various ­scenarios.”

Japan Olympics Minister Seiko Hashimoto said she was “glad to hear” that the IOC was not considering canceling the Games, and Mori said the IOC and Japan would like to “closely examine” the various scenarios.

For athletes, ambiguity regarding postponement has led to frustration. They have continued to train as facilities have shuttered and governments have imposed restrictions. Over the weekend, USA Swimming and USA Track and Field called for the Games to be postponed, with USA Swimming specifically asking for a delay until 2021. Both federations cited protecting athletes’ physical and mental health. USA Gymnastics joined them Monday after polling athletes over the weekend. Sebastian Coe, head of World Athletics, the international governing body for track and field, responded to Bach’s letter Sunday by writing to him and saying the current schedule is “neither ­feasible nor desirable.”

Germany on Monday became the latest country to announce that it would not send athletes to Tokyo this summer. Michael Schirp, a spokesman for the German team, said about 200 German athletes participated in a teleconference Saturday evening with the country’s top Olympic officials to voice their concerns. They were given a survey to complete, gauging their willingness to compete this summer. Their feelings were supposed to guide the German response, Schirp said, but after the IOC said a decision could take another four weeks, Alfons Hörmann, head of Germany’s Olympic committee, decided he had to act sooner.

Britain subsequently joined the chorus.

“If the virus continues as predicted by the Government, I don’t think there is any way we can send a team,” British Olympic Association chair Hugh Robertson told Sky Sports.

Beyond determining what is feasible from a public health standpoint, postponement would be an enormously complicated undertaking.

For each scenario, organizers would have to work out whether they could still secure the Olympic venues for all 33 sports, as well as for the Paralympics, and what the costs would be. There are also doubts about the availability of some sites, including the Olympic Village, where hundreds of apartments have been sold by a consortium of real estate developers for occupancy after the Games had been scheduled to conclude Aug. 9, and the planned media headquarters at Tokyo Big Sight, a tightly booked conference center.

“We have to go through each of them one by one,” Mori said. “Considering just these things alone would take an enormous time.”

Mori hinted that organizers would prefer to keep the Olympics within this calendar year when he said, “We are 2020, so that is the direction for now.”

For athletes, the length of a delay would alter drastically who is able to qualify or excel, with wide varieties depending on the sport. A long delay could mean some aging veterans miss the chance at a final Olympics. Some athletes, particularly female gymnasts, have small windows during which they are the best in the world and might prefer to compete closer to the time at which they had been preparing to peak.

NBC executives also have been in conversation with Olympic officials, and their wishes carry weight. More than 70 percent of the IOC’s nearly $6 billion from the current four-year Olympic cycle comes from TV revenue. Of that, NBC and parent company Comcast pay around half of it.

One former NBC executive believed the company would be satisfied with postponing the Games exactly a year. A shorter postponement — into the fall of this year, for instance, would force the Olympics to compete with football and a number of other events that already have been pushed from this spring, such as the Masters golf tournament.

For now, organizers say they will push ahead with the torch relay, which is set to start Thursday in Fukushima in northeastern Japan and is meant to symbolize Japan’s recovery from a 2011 tsunami and nuclear accident in the area. Mori said the prime minister was unsure whether he would attend the start of the relay — the government wanted to discourage crowds forming — although Mori said he himself would attend.

Mori acknowledged the relay route may need to be modified and said organizers were studying how it should be held given the fast-changing situation with the virus.

Tens of thousands flocked to a stadium in Sendai north of Tokyo to see the Olympic flame burning in a cauldron over the weekend after it arrived from Greece.

“We had a turnout nearly 10 times that we had estimated,” ­Tokyo 2020 CEO Toshiro Muto said.

Muto said organizers should be happy with the turnout “in and of itself” but had placed risk as their top priority and had changed arrangements so people simply passed by the flame without a crowd forming.

Denyer reported from Tokyo. Akiko Kashiwagi in Tokyo and Ben Strauss in Washington contributed to this report.