ISTANBUL — Antigovernment protests spurred by economic woes hit Iran for a third straight day Saturday, in what has quickly emerged as a significant challenge to the administration of President Hassan Rouhani.

Demonstrators protesting price increases and high unemployment turned out in cities and towns across the country, defying police and voicing anger at the cleric-ruled government, in an extraordinary display of public dissent.

Earlier Saturday, thousands of supporters of Iran’s ruling clerics rallied around the country, but antigovernment protests in several major cities showed no signed of abating.

Just hours after hard-liners wrapped up their gathering in Tehran, college students and others turned out for another spontaneous rally against the government, the Associated Press reported.

About 4,000 people took part in the progovernment rally in Tehran, state media reported, adding that similar rallies were held in more than 1,200 cities and towns.

The rallies were originally planned to mark the end of the 2009 uprising, a reform movement crushed by government hard-liners. But they took on new significance after unrest was reported in several Iranian cities Thursday and Friday, including Tehran, the capital; Mashhad, Iran’s second largest city; Kermanshah in the west; and Qom in the north.

Demonstrators in those protests set out to voice objection to rising prices but were soon chanting against Iran’s government, an unusual show of public dissent. Footage uploaded to social media showed protesters defying security forces.

Police used tear gas and water cannons to disperse protesters, Iranian human rights groups reported. At least 50 people were arrested, authorities said.

Official media for the most part ignored the widespread protests, which targeted Rouhani and even Ayatollah Ali Khamenei, the supreme leader, who has the final say on all foreign and domestic policy matters.

The opposition protests in Tehran, as well as President Trump tweeting about them, prompted state television to break its silence.

‘‘Counterrevolution groups and foreign media are continuing their organized 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.

Hundreds of students and others joined the new economic protest at Tehran University on Saturday, with riot police massing at the school’s gates as they shut down nearby roads.

The protesters chanted slogans against high-ranking government officials and made other political statements, according to the semiofficial Fars news agency.

Protesters shouted, “Death to the dictator’’ and “Clerics should get lost,’’ witnesses said. Referring to the supreme leader, others chanted: “Shame on you, Seyyed Ali Khamenei. Let the country go.’’

Some protesters burned a banner with an image of his face.

Trump tweeted support for the protesters early Saturday, saying the government should respect the people’s right to express themselves. “The world is watching!’’ Trump said.

‘‘The entire world understands that the good people of Iran want change,’’ Trump said in a later Twitter message. ‘‘Iran’s people are what their leaders fear the most.’’

A spokesman for the Ministry of Foreign Affairs, Bahram Qassemi, condemned the remarks by the president as “meddlesome’’ and “opportunistic.’’

It’s unclear what effect Trump’s support would have.

Iranians are largely skeptical of him over his refusal to recertify the nuclear deal and Iran being included in his travel bans. Trump’s insistence in an October speech on using the term ‘‘Arabian Gulf’’ in place of the Persian Gulf also has also riled the Iranian public.

On Saturday, social media videos emerged of earlier antigovernment demonstrators at Tehran University, and in Kermanshah, where hundreds of people were killed in a major earthquake last month.

Iran’s interior minister Saturday warned citizens against joining ‘‘illegal gatherings,’’ according to the semiofficial ISNA news agency.

The Revolutionary Guards, which along with its Basij militia spearheaded a crackdown against protesters in 2009, said in a statement carried by state news media Saturday that efforts were underway to replicate that unrest, and that Iran “will not allow the country to be hurt.’’

The government has shown little restraint in brutally quelling dissent, and many analysts speculated the protests would fizzle. But they also warned that harsh measures from security forces could spark further anger, leading to more demonstrations.

Iranians have struggled under an ailing economy they hoped would soar after the country reached a nuclear deal with world powers and major international sanctions were lifted.

Iran’s economy has grown since the deal was struck in 2015, in large part thanks to the country’s renewed oil exports.

But its non-oil economy has failed to keep up, hindering broader job creation, economists say.