It also placed some restrictions on access to major Shia Muslim shrines in Qom, the epicentre of the country's Covid-19 outbreak, and Mashhad.

The Iranian health ministry meanwhile warned that the number of cases would continue to rise in the coming days.

It reported 388 confirmed cases and 34 related deaths on Friday.

The death toll is by far the highest outside China, and the World Health Organization (WHO) has warned that the outbreak may be worse than realised.

Iran has also been the source of dozens of cases in neighbouring countries, including Afghanistan, Bahrain, Iraq, Kuwait, Oman and Pakistan.

There have been 82,000 reported cases of Covid-19 worldwide and 2,800 deaths since the disease emerged late last year. All but 3,664 cases and 57 of the deaths have been reported in China.

More than 900 cities and towns across Iran hold weekly Friday prayer services, during which imams designated by the supreme leader deliver sermons.

Thousands of people would have been expected to attend those in the 23 provincial capitals that were cancelled on the advice of the health ministry.

The ministry also called for restrictions on access to the Hazrat Masumeh shrine in Qom and the Imam Reza shrine in Mashhad, which are both visited by millions of Shia pilgrims every year.

Health Minister Saeed Namaki told state TV on Wednesday that people would be allowed to visit the sites once they had been given hand-sanitising gels, health information and face masks.

"[They must] not gather together in groups - just pray and leave," he said.

The Hazrat Masumeh shrine in Qom is being disinfected regularly, but not closed

Senior Shia clerics have rejected calls for the shrines to be closed since the first case of Covid-19 was reported in Iran nine days ago.

The custodian of the Hazrat Masumeh shrine, Ayatollah Mohammed Saeedi, said on Wednesday that it should be kept open as a "house for cure" and that "people should be encouraged to come".

On the same day, President Hassan Rouhani ruled out locking down any cities or districts, saying that the authorities would continue to "only quarantine individuals".

Vice-President for Women's and Family Affairs Masoumeh Ebtekar became the latest Iranian official to be infected on Thursday.

The Hamshahri Online website reported that Ms Ebtekar - the highest-ranking woman in the Iranian government - had attended a meeting with President Hassan Rouhani and a number of ministers shortly before testing positive.

Deputy Health Minister Iraj Harirchi and at least four members of parliament have also been infected, while the prominent cleric Hadi Khosroshahi died on Thursday.

Image copyright AFP

Image caption The outbreak has affected high-profile politicians, including Vice-President Masoumeh Ebtekar

In a letter to the supreme leader on Thursday, Mr Namaki defended Iran's response the Covid-19 outbreak and predicted that the country "without any question, would surprise the entire world when the disease is brought to its knees".

But on Friday health ministry spokesman Kianoush Jahanpour cautioned that "the rate of coronavirus infection would continue to rise in the coming days".

"Staying home, restricting traffic, reducing movement and interactions, avoiding unnecessary travel, cancelling any nationwide gatherings along with observing individual health tips are the only ways to control Covid-19," he tweeted.

The head of the WHO's emergencies programme said on Thursday that the apparent high mortality rate in Iran indicated its outbreak might be more widespread than realised.

"The most likely factor is that obviously this disease came unseen and undetected into Iran so the extent of infection may be broader than what we are seeing," Dr Michael Ryan told reporters.

"There is a very high clinical capacity for managing severely ill patients in Iran, so I don't suspect this has anything to do with clinical care," he added.

A WHO mission is due to arrive in Iran early next week to advise local officials.