IRANIAN hard-liners rallied in support of the country's supreme leader and clerically overseen government as spontaneous protests sparked by anger over the ailing economy hit major cities in the Islamic Republic.

The demonstrations, commemorating a mass 2009 pro-government rally challenging those who rejected the re-election of hard-line president Mahmoud Ahmadinejad amid fraud allegations, had been scheduled weeks earlier.

However, they took on new importance after the economic protests began on Thursday, sparked by social media posts and a surge in prices of basic food supplies, like eggs and poultry.

Thousands took to the streets of several cities in Iran, beginning in Mashhad, the country's second-largest city and a holy site for Shiite pilgrims. Demonstrators have also criticised Iran's government during the protests, with social media videos showing clashes between protesters and police.

Protests on Friday were reported to have struck Qom, the world's foremost centre for Shiite Islamic scholarship and home to a major Shiite shrine.

The demonstrations appear to be the largest in the Islamic Republic since its 2009 Green Movement arose after Ahmadinejad's re-election.

However, information about them remains scarce as both state-run and semi-official media in Iran have not widely reported on the protests.

An online report by Iranian state television this weekend said national media in the country had not reported on the protests on orders from security officials.

State TV also aired its first reports on the protests today, acknowledging that some protesters chanted the name of Iran's one-time shah, who fled into exile just before its 1979 Islamic Revolution.

"Counter-revolution groups and foreign media are continuing their organised efforts to misuse the people's economic and livelihood problems and their legitimate demands to provide an opportunity for unlawful gatherings and possibly chaos," state TV said.

It broadcast live today's pro-government "9 Dey Epic" demonstrations, named after the date on the Iranian calendar when the 2009 protests took place. The footage showed people waving flags and carrying banners bearing the image of Iran's Supreme Leader, Ayatollah Ali Khamenei.

In Tehran, some 4000 people gathered at the Musalla prayer ground, calling for criminal trials for Mir Hossein Mousavi and Mahdi Karroubi, leaders from the Green Movement who have been under house arrest since 2011.

Iranian President Hassan Rouhani, whose administration struck the 2015 nuclear deal with world powers, campaigned on freeing the men, though they remain detained.

Mohsen Araki, a Shiite cleric who serves in Iran's Assembly of Experts, praised Rouhani's efforts at improving the economy. However, he said he needed to do more to challenge "enemy pressures".

"We must go back to the pre-nuclear deal situation," said Araki. "The enemy has not kept with its commitments."

Ali Ahmadi, a pro-government demonstrator, blamed the US for all of Iran's economic problems.

"They always say that we are supporting Iranian people, but who should pay the costs?" he asked.

By this afternoon, hundreds of students and others joined a new economic protest at Tehran University. Witnesses said they saw a mass of riot police at the gates of the university, while some roads had been blocked off.

Iran's economy has improved since the nuclear deal, which saw Iran limit its enrichment of uranium in exchange for the end of some of the international sanctions that crippled its economy. Tehran now sells its oil on the global market and has signed deals for tens of billions of dollars of Western aircraft.

That improvement has reached the average Iranian, but unemployment remains high. Official inflation has crept up to 10 per cent again.

A recent increase in egg and poultry prices by as much as 40 per cent, which a government spokesman has blamed on a cull over avian flu fears, appears to have been the spark for the protests.

While police have arrested some protesters, the country's powerful Revolutionary Guard and its affiliates have not intervened as they have in other unauthorised demonstrations since the 2009 election. The economic protests initially just put pressure on Rouhani's administration, but purported footage from recent demonstrations has included anti-government chants.

US President Donald Trump tweeted his support for the protests earlier today.

"Many reports of peaceful protests by Iranian citizens fed up with regime's corruption & its squandering of the nation's wealth to fund terrorism abroad," he wrote. "Iranian govt should respect their people's rights, including right to express themselves. The world is watching! #IranProtests."

It was unclear what effect Trump's support would have. Iranians are largely sceptical of him over his refusal to re-certify the nuclear deal. His insistence in an October speech on using the term "Arabian Gulf" in place of the Persian Gulf has also riled the Iranian public.

Meanwhile, US Secretary of State Rex Tillerson's comments in June to Congress saying America is working towards "support of those elements inside of Iran that would lead to a peaceful transition of that government" has been taken by Iran's government as a sign of foreign interference in its internal politics.

The State Department issued a statement on Friday supporting the protests, referencing Tillerson's earlier comments.

"Iran's leaders have turned a wealthy country with a rich history and culture into an economically depleted rogue state whose chief exports are violence, bloodshed and chaos," the statement said.