The International Olympic Committee says it is premature to speculate about taking the 2016 Games away from Brazil, despite sports federations demanding a "Plan B" because of chronic delays in Rio de Janeiro.
But IOC president Thomas Bach and other Olympic officials said the construction hold-ups and political paralysis have reached a critical point, requiring the IOC to take special measures to save the Games.
"It's about time for action," Bach said following an unprecedented public outpouring of criticism and complaints from international sports leaders about the lack of progress in Rio.
Several sports federations asked about contingency plans for their venues and one - handball - asked if there was a backup for the Games themselves if Rio won't be ready on time.
Asked whether there had been discussion on moving the Games out of Brazil, IOC spokesman Mark Adams stopped short of ruling it out.
"At this stage, that would be far too premature," he said. "We're not talking about Plan B. We're still talking about delivery of the Games."
"The IOC has outlined its concerns for some time now - that time is running out," Adams said after Rio organisers spoke to the executive board by video conference.
"We believe that Rio 2016 can still deliver a good Games if appropriate action is taken immediately. The clock is ticking. Every day is crucial, but they can still deliver."
With two years to go, relocating the Games would be a last resort, and finding an alternate site at such short notice would be virtually impossible.
However, raising alarms about Rio's state of readiness serves to ramp up the pressure on the Brazilians.
Rio organisers issued a statement from Brazil after talking with the executive board.
"We are fully aware of the issues that need to be resolved," the statement said. "We are grateful for the input from all stakeholders.
"Progress has been made in the past two weeks, since the last visit of the IOC Coordination Commission for Rio 2016. We move ahead every single day. There is absolutely no question in our minds that Rio will deliver great Games."
Leaders of 18 different federations spoke out about Rio's troubled preparations in a meeting with Bach and the IOC executive board. All but one - volleyball - raised serious concerns.
The greatest worry centres on Deodoro, a complex in north Rio that is to host venues for eight sports. Work has not even begun on the site.
"The general feeling is that we are in the most critical situation in the preparation for the Games that has happened in the last 20 years at least," said Francesco Ricci Bitti, head of the Association of Summer Olympic International Federations.
IOC vice-president Craig Reedie said the problems in Rio appeared greater than those for the 2004 Athens Olympics, where serious concerns lingered up to the last minute.
"There was pressure on Athens to finish construction and to deliver, but they did and there was a feeling that, although it was tight, it would always be done," Reedie said. "Some of the federations are now saying, 'Look they [Rio] haven't started building, so can they actually finish this one on time?"
Ricci Bitti said the sports raising the issue of a "Plan B" were referring to venue plans, not moving the Games.
"We are not at this stage," he said, adding that basketball, for example, could consider playing some games in Sao Paulo if the Deodoro venue will not be ready.
Bach said he was waiting for more details of the meeting in Brasilia between Rio organisers and President Dilma Rousseff's chief of staff.
Brazil's sports ministry said the deadlines would be met "and the Games themselves would take place without disorder".
Ricci Bitti said the Olympic project was in danger of falling further behind because of the upcoming soccer World Cup in Brazil and a presidential election in October.
"We require you to take action immediately," the Italian told Bach. "We cannot waste these next six months."
The Deodoro complex would be used by shooting, equestrian, modern pentathlon, canoe slalom, rugby, basketball, cycling and field hockey.