Brazil's sports ministry confirmed no tests were carried out between July 1 and July 24 due to a World Anti-Doping Agency (WADA) suspension on a drug-testing laboratory in Rio de Janeiro, The Times reported on Friday.
WADA said it was "concerned" and had sent a letter to Brazil's sports minister asking why the tests had been stopped.
"We sent a letter to the minister of sport and the executive director of the Brazilian national anti-doping agency, pressing our concerns and demanding to know why testing had been stopped in Brazil," WADA deputy director Rob Koehler told the newspaper.
"The response was not satisfactory... the explanation that it had come about due to the changing of the guard in the ministry and the agency was not acceptable to us.
"We informed the pre-Games task force and we told them to ramp up increased tests. It was unacceptable that it stopped. That was not a good move... the fact no testing was happening was a concern."
South America's first Olympics have been mired in a drugs scandal with Russia's track-and-field athletes and weightlifters barred from the Rio Games over doping offences.
The European country narrowly avoided a complete ban over allegations its government and FSB security service systematically covered up widespread cheating.
The International Olympic Committee (IOC) chose not to impose a blanket ban on all Russian athletes but directed sports federations to allow them to compete if they met a set of criteria, including a clean doping past and sufficient testing at international events.
Luis Horta, the former head of Portugal's anti-doping agency who was given a role as an adviser to Brazil, alleged he faced pressure from the country's sports ministry and Olympic committee to reduce testing.
A statement from Brazil's sports ministry refuted the allegations, while adding that three overseas laboratories were approached but were unable to help with the testing of samples.
"The Ministry of Sport and the Brazilian Doping Control Authority strongly refute the accusations made by Mr Horta," it said.
"With the suspension imposed by WADA to the laboratory on June 22, the tests planned for the period between 1 and 24 July were compromised (the suspension was only lifted on July 20), as analyses could not be submitted.
"Therefore, the planned tests ended up not being done in that period."
Marcus Vinicius Freire, executive director of the Brazilian Olympic Committee (COB), said on Friday that his organisation asked for a reduction of tests because Brazilians were being subject to up 12 a month when top-ranked athletes elsewhere had to take only three.
The high number of tests was in part because of a need to train technicians at the Brazilian lab that will be used for the Olympics doping tests, he said.
"My conversation with the ABCD was in the sense that they do the training tests with athletes that are not preparing for the Olympics, to protect anybody, but because our athletes were being tested way more than normally," Freire said.
(Writing by Sudipto Ganguly in Mumbai and Jeb Blount in Rio de Janeiro, additional reporting by Pedro Fonseca in Rio de Janeiro; editing by Ed Osmond)
