Rio’s anti-doping laboratory has been suspended by the World Anti-Doping Agency (Wada) just six weeks before the Brazilian city hosts the Olympic Games.
The ban was imposed because it fails to comply with international standards.
Rio’s is the sixth laboratory to be sanctioned by Wada in recent months.
Madrid, Bloemfontein, Beijing and Lisbon have also been suspended from Wada-related activities, while Moscow’s laboratory had its accreditation revoked in April.
Rio’s suspension took effect on 22 June and prohibits the laboratory from carrying out all anti-doping analyses on urine and blood samples.
The lab may appeal against the decision to the Court of Arbitration for Sport within 21 days of receipt of notice.
“Athletes can have confidence that the suspension will only be lifted by Wada when the laboratory is operating optimally,” said Wada’s incoming director general Olivier Niggli.
“The best solution will be put in place to ensure that sample analysis for the Rio Olympic and Paralympic Games is robust.”
Exactly how the laboratory, also known as Ladetec, has failed to comply with Wada standards was not revealed – but it is not the first time the anti-doping body has punished it.
In January 2012 Ladetec was suspended from testing for nine months for falsely accusing a Brazilian beach volleyball player of doping.
Its license was also suspended for not complying with international standards in August 2013 and its accreditation revoked a month later, meaning Rio did not have a functioning anti-doping lab for the duration of the football World Cup in 2014.
The nearest alternative Wada-accredited facility to Rio is 2,800 miles away in Bogota, Colombia.