The first two athletes to test positive for coronavirus in Tokyo's Olympic Village have been confirmed as members of South Africa's men's football team.
Games organizers announced in their daily update on Sunday that there had been 10 positive cases in the latest round of testing, taking the overall total this month to 55.
That includes three individuals based in the athletes' village, with an event official previously testing positive on Saturday.
The South African Football Association released a statement later on Sunday confirming Thabiso Monyane and Kamohelo Mahlatsi were the pair to return positive tests.
Orlando Pirates right-back Monyane and Moroka Swallows attacking midfielder Mahlatsi, plus video analyst Mario Masha, will now isolate in a hotel room for 14 days.
A fourth South African participant, rugby sevens coach Neil Powell, also produced a positive result. All four individuals tested negative before flying to Japan this week.
Team South Africa chief medical officer Dr Phatho Zondi said in a statement: "Every member of Team South Africa required full medical clearance as an eligibility criteria.
"In addition, they were encouraged to isolate for two weeks pre-departure, monitor health daily, report any symptoms, and produce two negative nasopharyngeal PCR tests taken within 96 hours of departure, as per Tokyo 2020 requirements.
"The timing of the positive results suggests that the PCR test in these individuals was done during the incubation period of the infection, which is how they could be negative in South Africa and then positive in Japan.
"They are now in isolation where they will continue to be monitored and will not be allowed to train or have any physical contact with the rest of the squad."
South Africa are scheduled to face tournament hosts Japan in their opening Group A game next Thursday, before taking on France and Mexico on July 25 and July 28 respectively.
Sunday's news of two athletes testing positive for COVID-19 inside the athletes' village will raise further concerns over the Olympics going ahead as planned.
The 2020 Games, already delayed by a year due to the global health pandemic, officially begins on Friday and will be held mostly without spectators due to a state of emergency being declared in Tokyo.
Infection rates in the Japanese capital have topped 1,000 for four days running.
Around 11,000 athletes from 205 national Olympic committees are expected to stay at the village over the next three weeks.
International Olympic Committee president Thomas Bach reiterated on Saturday that the first positive case posed no risk to the Japanese population.
"We are well aware of the scepticism a number of people have here in Japan," he added at a news conference. "My appeal to the Japanese people is to welcome the athletes for their competitions."