"Unfortunately, in the past 24 hours [from Sunday to Monday], we have lost 203 of our compatriots due to the COVID-19 disease," said Health Ministry spokeswoman Sima Sadat Lari.
"Based on this figure, the total number of victims has reached 13,032," she told a televised news conference.
Isa Jafari, an Iranian lawmaker, also died of COVID-19 on Monday in a hospital in the capital, Tehran.
Lari said another 2,349 people had tested positive for the virus, raising the overall figure in the country's outbreak to 259,652.
Of the new cases detected, 1,581 patients have been admitted to the hospital, the spokeswoman said.
At least 222,539 patients have recovered from the coronavirus infection so far or have been discharged from hospitals across Iran, she said.
Among those undergoing treatment in medical centers at present, 3,375 coronavirus patients have critical health conditions because of more severe infection, Lari noted.
The spokeswoman also said more than 1,997,000 coronavirus diagnostic tests have been carried out in Iran so far.
Iran has been struggling to contain the virus since announcing its first cases in February – two deaths in the city of Qom.
Official figures have shown an upward trajectory in new confirmed cases since early May, when Iran hit a near two-month low in daily recorded infections.
The Iranian government made the wearing of masks compulsory in closed public spaces from July 4, including on public transport.
State television said on Monday that police in Tehran were stopping commuters without masks from entering the subway.
Authorities in Qom tightened controls in banks and administrative offices to ensure the implementation of health protocols, including mask-wearing.
The Health Ministry spokeswoman called on everyone to keep a physical distance from others, to wash their hands and to use masks.
"The more time you spend in an overcrowded environment, the more likely you are to contract the disease," Lari said.
Iran closed schools, canceled public events and banned movement between its 31 provinces in March, but progressively lifted restrictions from April to try to reopen its economy.
IRNA, Tasnim News Agency, and AFP contributed to this story.