Japanese authorities were searching for a Ugandan weightlifter on Friday after he went missing just a week before the Tokyo Olympics, which have sparked public opposition over their coronavirus risks.
Julius Ssekitoleko, 20, who was taking part in a training camp near Osaka, failed to turn up to a Covid-19 test and was not in his hotel room.
His disappearance comes with intense scrutiny in Japan over the risk of virus infections spreading from the postponed 2020 Games, as cases surge in the country.
On Friday, the government said it had asked organisers to investigate reports of Games participants breaking virus rules, a day after Olympic chief Thomas Bach insisted the regulations "are working, and they are enforced".
Among thousands of Games-related arrivals in July, only a handful of positive cases have been recorded.
But ahead of the opening ceremony on July 23, Tokyo is under a virus state of emergency and has in recent days recorded its highest infection numbers since January.
Organisers have been forced to bar spectators from all events in Tokyo and most venues elsewhere, while athletes, officials and staff face strict anti-virus measures including regular testing and limits on their movement.
Ten positive cases, including one athlete, have emerged among Games participants in the past two days.
Further cases have been found among teams arriving for training camps, with Japanese media reporting Friday that a member of Nigeria's delegation had been hospitalised after testing positive at the airport.
Ssekitoleko's disappearance in Izumisano city comes after two members of Uganda's delegation tested positive in Japan, including a coach who was isolated at the airport.
"The city is making all efforts to search for the individual. We have reported the matter to police," a statement from city authorities said.
Salim Musoke Ssenkungu, president of the Ugandan Weightlifting Federation, told AFP that Ssekitoleko had been training "very hard" for his first Olympic weightlifting competition but was told this week that he would not be allowed to compete and had to return home.
"If someone is there in Japan and is assuming he is going to compete but then gets bad news, of course he is going to be upset," Ssenkungu said.
The young athlete had recently won a bronze in the Africa Weightlifting Championships and was considered experienced despite his youth, he added.
"He's not from a rich family so it took a lot of interest and energy from him to be successful," Ssenkungu said.
Donald Rukare, president of the Uganda Olympic Committee, said officials had only just been informed about the disappearance.
"We are also trying to find out (what happened). We are in contact with the team in Osaka," he told AFP.
Uganda's delegation arrived in Japan last month, headed for a pre-Games training camp in Izumisano, in Osaka region.
Japan has seen a smaller Covid-19 outbreak than many countries, with fewer than 15,000 deaths despite avoiding harsh lockdowns, but only around 20 percent of the population is fully vaccinated so far.
'Feels like we're in prison'
Dozens of teams are already in Japan -- some at training camps dotted around the country, and others in the Olympic Village, where national flags have been hung on the buildings housing delegations.
However, Australian basketball star Liz Cambage announced her withdrawal over the mental health risks of staying in "terrifying" bubble conditions.
"No family. No friends. No fans. No support system outside of my team. It's honestly terrifying for me," the four-time WNBA All-Star said in a statement.
British weightlifter Sarah Davies said living in the bubble felt like "prison".
"We have what we call the prison yard," she said in a video posted on her Instagram account as she walked on a stretch of pavement.
"So we can literally walk up and down this stretch between the hours of 7 am and 10 am, and that is the only time we're allowed outside," she said.
"Genuinely, feels like we're in prison. But, hey, it is what it is... Welcome to Olympic Games, Covid edition."
Olympic officials are also in Japan, including Bach who visited Hiroshima on Friday to mark the start of an "Olympic truce" that urges a worldwide halt to hostilities during the Games.
The visit sparked some controversy, with more than 70,000 people signing a petition opposing his trip and accusing Bach of using Hiroshima and Nagasaki "to promote the Olympics... even though it is being forced through despite opposition".
Polls have shown most Japanese want to see the Games postponed or cancelled, though some recent polls showed opposition softening.
The German former fencer laid a wreath at a memorial to victims of the atomic bombing in Hiroshima, and appeared shaken after visiting a museum documenting the attack and its aftermath.
Describing himself as "humbled" by the trip, Bach said the Games would "be a beacon of hope for a better and more peaceful future".
Bach has been meeting local officials in recent days and Japanese media said Friday he had asked the prime minister to consider allowing spectators into Olympic venues if the virus situation improves.
Up to 5,000 spectators are currently allowed at non-Olympic sporting events in Tokyo, despite the emergency.
But officials argue the Games is different because it involves multiple events happening simultaneously, posing a greater risk of crowds gathering and infection spreading.