Two South African football players have become the first athletes to test positive for coronavirus in the Olympic Village.
The South African Football Association confirmed the two players to receive positive tests were Thabiso Monyane and Kamohelo Mahlatsi.
A Games official was the first individual based in the Olympic Village to test positive on Saturday, on the same day IOC president Thomas Bach insisted the Games will be "safe and secure".
South African video analyst Mario Masha and rugby sevens coach Neil Powell have also tested positive, taking the total number of confirmed infections for the country to four.
Powell tested positive on arrival in Japan and is in isolation in Kagashima where the sevens squad are at a pre-Games training camp.
South Africa team manager Mxolisi Sibam said in a statement: "Masha and Monyane reported high temperatures and positive saliva tests, and were then taken to do the nasal test...and they unfortunately tested positive for Covid-19."
Twenty-one people within the South Africa team have been identified as close contacts and are isolating in their rooms.
South Africa are due to plan Japan in one of the two opening matches of the men's tournament on Thursday.
Team chief medical officer Dr Phatho Zondi said they were surprised at the infections, but he believes all protocols have been followed for the country's athletes competing at the Games.
"Every member of Team South Africa required full medical clearance as an eligibility criteria," Zondi said in a statement.
"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(s)."
The Sevens rugby competition, where South Africa will be among the favourites, begins on July 26.
IOC president Bach said on Thursday the risk of the Japanese public being infected with the virus by a Games participant is "zero".
However, there is rising nervousness in Tokyo after the city recorded over 1,000 new cases for the fourth straight day.
In a press conference on Sunday, IOC executive director Christophe Dubi appeared to backtrack, admitting: "There is no such thing as zero risk.
"At the same time, mingling with the population is incredibly limited. We can ensure that the transmission between the various groups is almost impossible.
"With all the measures that are in place, including the separation at the Olympic Village, we keep the risk at an absolute minimal level."
Last week, the South African rugby sevens team were forced to quarantine for four days due to being considered close contacts of a passenger who tested positive on their flight to Tokyo.
Meanwhile, the IOC Refugee Team has delayed its arrival in the Japanese capital from its training camp in Qatar after a member of its delegation tested positive.