The governing body of American athletics, USA Track and Field, has called for a postponement of the Tokyo Olympics due to fears over the coronavirus pandemic.
The Brazilian Olympic Committee (COB), meanwhile, called for this year's Games to be suspended until 2021.
In a letter to United States Olympic & Paralympic Committee (USOPC) chief executive Sarah Hirshland, the federation asked the International Olympic Committee (IOC) to postpone the Games which are scheduled to run from July 24-August 9.
"We certainly understand the ramifications of this request, and the realities of trying to coordinate the logistics of a postponed Olympic Games around the schedules of other athletes, sport federations, key stakeholders etc, but the alternative of moving forward in light of the current global situation would not be in the best interest of our athletes [as difficult as that decision might be]," USATF chief executive Max Siegel said in the letter.
Brazil urged the IOC to follow in the footsteps of Uefa and Conmebol, the governing bodies of football in Europe and South America, in delaying the Olympics for 12 months.
"As an ex-judoka and coach in the sport, I learned that every athlete’s dream is to go to the Olympics in top form,” said COB president Paulo Wanderley.
"It’s clear that right now maintaining the games for this year will impede this dream from being fully realised.”
The COB stressed it still had full confidence in the IOC but said a move was the best solution.
“The IOC has gone through immense problems before, with the episodes that ended in the cancellation of the games in 1916, 1940 and 1994, because of the world wars, and the boycotts of Moscow 1980 and Los Angeles 1984,” Wanderley said in quotes posted on the COB website.
"They knew how to overcome these obstacles and the Olympic flame is stronger than ever.”
The USA track federation is the latest American sports organisation seeking a delay to the Games, after USA Swimming voiced its concerns for athlete, staff and public welfare earlier this week.
France's swimming federation added to the mounting pressure on the IOC to act, saying "The current context does not allow the 2020 Olympic Games to be organised properly".
US Olympic officials are yet to respond to the USATF's request while the IOC were not immediately available for comment.
The US committee said on Friday that athletes should continue their preparations amid the coronavirus pandemic that has now infected more than 250,000 people worldwide and claimed more than 11,000 lives.
Meanwhile, the IOC has pressed on during the health crisis, saying the Games will go ahead as scheduled.
The issue has sharply divided athletes globally and USATF said no decision should be made at the expense of the safety and well-being of its athletes.
"We acknowledge that there are no perfect answers, and that this is a very complex and difficult decision, but this position [to postpone the Games] at least provides our athletes with the comfort of knowing that they will have adequate time to properly prepare themselves physically, mentally and emotionally to be able to participate in a safe and successful Olympic Games," it said.
"We urge the USOPC, as a leader within the Olympic Movement, to use its voice and speak up for the athletes."
