The International Olympic Committee has sent a clear warning to the organisers of the Rio 2016 Games that "every second counts" after visiting the Brazilian city.
With just over two years to go, the IOC said that a "constant, concerted and integrated effort is required for the successful delivery of the Games and its legacy".
It added: "Although progress is being made, each decision that is postponed and each subsequent delay will have a negative impact on delivery. Total focus and dedication are therefore required."
ITV News' Brazil correspondent Nick Ravenscroft, who was at the news conference, tweeted:
Argentinian protesters have burned an effigy of the Queen amid anti-British demonstrations ahead of an announcement of the host city for the 2020 Olympic Games in Buenos Aires.
Around 250 demonstrators burned flags and chanted against British involvement in the International Olympic Committee (IOC).
The IOC will elect the host city for the 2020 Summer Games later today, deciding between bids from Istanbul, Madrid and Tokyo.
The International Olympic Committee (IOC) has dropped wrestling from the 2020 Olympic Games.
The IOC's ruling committee looked at a number of sports and decided to retain the modern pentathlon - which was viewed as being most at risk - and remove wrestling instead.
It will now have to compete with other sports including baseball/softball, squash and karate to be added back into the programme when the full IOC session meets in September.
IOC communications director Mark Adams told a news conference, "The executive board recommended that wrestling not be included on the list of 25 core sports and it now joins shortlisted sports vying for inclusion on the 2020 Olympics programme as an additional sport".
The International Olympic Committee said the Syrian athlete Ghfran Almouhamad has tested positive for a banned substance.
International Olympic Committee chairman Denis Oswald has announced that "London is ready to welcome the World."
Mr Oswald made the announcement at a news conference following the IOC's final inspection of London ahead of the Olympics this summer.