Tanzanian President John Magufuli on Sunday questioned his country's coronavirus numbers, and called on the authorities to investigate "sabotage" at the national laboratory.
The East African country had recorded 480 cases of the virus and 16 deaths at its last update on Wednesday.
The government has come under fire from the opposition for allegedly hiding information and failing to take the disease seriously.
Magufuli said that people who tested positive for the virus may not be sick, and cast doubt on the credibility of laboratory equipment and technicians.
"The equipment or people may be compromised and sometimes it can be sabotage...," Magufuli said in a Swahili speech broadcast live through state-run TBC.
Papaya and goat 'tested positive'
He said he had secretly had a variety of animals, fruits and vehicle oil tested at the laboratory.
According to Magufuli, a papaya, a quail and a goat tested positive and he suspects a "dirty game" in the laboratory.
"That means there is possibility for technical errors or these imported reagents have issues. Probably, the technicians are also bought to mislead."
Magufuli was swearing in the new Minister for Constitution and Legal Affairs Mwigulu Nchemba, and urged him to "go and investigate if there is criminal possibility at the national laboratory and take action".
Nchemba is taking over after the death of Augustine Mahiga -- one of three MPs who died in the space of 11 days.
No reasons were given for the lawmakers' deaths.
However one MP tested positive for the coronavirus in April, and the opposition announced Friday it was ordering its lawmakers to stop going to parliament and to isolate themselves after the string of deaths.
Tanzania is one of a few countries in Africa that have not taken extensive measures against the virus, and Magufuli is among a handful of world leaders still playing down the seriousness of the disease.
Schools and universities have been shut but markets, bus stops and shops bustle as usual, with Magufuli urging citizens to continue working hard and not stop going to church or mosques.
On Sunday he criticised a Muslim leader who on Friday shut a large mosque in Dar es Salaam as a precaution against the spread of the virus.
"It's strange to stop believers from entering a mosque which they built themselves. If you fear going there, let others go and pray. By the way we are still in the elementary stage of coronavirus," he said.
Magufuli also said Tanzania was in talks with Madagascar for a potion that the island nation claims cures COVID-19 patients within 10 days.