(CNN) The head of Iran's Revolutionary Guards said Wednesday that a string of anti-government protests were over after six days of unrest.

In comments to the semiofficial Fars news agency, Mohammad Ali Jafari said that only 15,000 people had turned out at the height of the rallies and that the main "troublemakers" have been arrested. CNN has not been able to verify the claim on the amount of protesters.

"Today, we can say it is the end of 'sedition 1396,' " Jafari said, using the year in the Iranian calendar.

"With the help of God, their defeat is definite," he said.

Jafari offered no evidence of how the movement had been defeated beyond the arrests, and his comments appeared to be a warning against more rallies.

The protests began last Thursday over Iran's stagnant economy and the rising cost of living but quickly have developed into a broader outcry against the government.

They have become the most powerful challenge to the Iranian government's authority since mass demonstrations in 2009.

The numbers turning out for rallies have dwindled in recent days, according to Los Angeles Times Tehran correspondent Ramin Mostaghim, but the protests continued Tuesday night in at least 10 cities.

Authorities have detained at least 450 people, and 21 others have been killed in the unrest.

Three members of the Revolutionary Guard Corps were killed dismantling an anti-government terrorist cell in northwestern city of Piranshahr, the state-run Islamic News Agency (IRNA) reported, citing Iran's Intelligence Ministry.

'An armed terrorist cell, which was assigned to explode and kill innocent people in order to keep the recent unrest going, had infiltrated Iran,' the Ministry said in a statement. One terrorist was killed and several others were injured during the raid.

Security forces also confiscated weapons, ammunition, and military uniforms that were to be used to 'provoke unrest,' IRNA reported.

Counterprotests through Iran

On Wednesday, thousands of government supporters marched through the capital, Tehran, state TV IRIB reported, with some chanting "Death to America" after Iranian officials blamed the United States and its allies for provoking the anti-government rallies.

Online state media reported a mix of people -- families, senior citizens and students -- were among the demonstrators, but images on television were mostly of middle-aged and older men. Many held pictures of Iranian President Hassan Rouhani and waved national flags.

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In contrast, the majority of anti-government protesters within the past week appeared to be young men, demanding more opportunities as unemployment and the cost of living remain relatively high.

Mojtaba, a 33-year-old Iranian who gave only his first name, told CNN that a lot of young people wanted the same lifestyles they see others having in wealthier parts of Iran as well as abroad.

"A lot of the kids in the smaller cities have gotten a taste for a better life through social media. They look at what they see on Instagram or Telegram and compare that to their prospects, and naturally they get angry."

The government has restricted those two apps in parts of the country but said they would be accessible again on Friday.

Friday will be a litmus test of how strong anti-government sentiment remains. When protests are staged in Iran, they often come after Friday prayers.

War of words

Officials in the United States and Iran have engaged in a fiery exchange of words over the unrest, triggered by President Donald Trump's tweets in support of anti-government protesters.

What's going on in Iran? By CNN's Nick Paton Walsh The pro-government protests reflect the comfortable re-election of moderate President Rouhani but also the voices of those who don't want to see continued upheaval in Iran. It is unlikely that continued and sustained unrest against the government would immediately result in a more moderate system taking its place -- Iran's hard-liners are quite capable of tackling dissent bluntly. Yet Wednesday's counter-groundswell doesn't negate what's behind the last week of unrest, or how unanticipated this has been. Yes, there have been smaller demonstrations in recent months against economic hardships, but few really thought so many would come out onto the streets for so long, or in so many cities. We've seen a coherent message emerge from the tougher elements of the Iranian government in the past two days: that "enemies" of Iran, namely the US, UK and Saudi Arabia, are behind this. The United States has done little to discourage that claim -- a senior State Department official revealed it's been in touch with protesters inside Iran via social media. President Donald Trump and his UN envoy, Nikki Haley, have openly encouraged protest, yet the White House has stopped just short of demanding regime change.

On Wednesday, Trump sent his third tweet on the matter : "Such respect for the people of Iran as they try to take back their corrupt government. You will see great support from the United States at the appropriate time!"

Nikki Haley, the US ambassador to the United Nations, doubled down on Trump's remarks on Tuesday and said that the United States was seeking emergency meetings with the UN Security Council and Human Rights Council.

"The people of Iran are crying out for freedom," Haley said. "All freedom-loving people must stand with their cause."

Iran's UN mission responded by calling Haley's comments "nauseous crocodile tears," according to a statement posted to the semiofficial Iranian Students News Agency.

"The Islamic Republic of Iran strongly condemned the meddlesome remarks made by Nikki Haley and other US officials concerning the riots in the country," it said. "The remarks are all part of Washington's attempts to mask its political failures and those of its allies in the region and to take revenge on the brave people of Iran."

Trump earlier had tweeted that the Iranian government was repressive, "brutal and corrupt" and that it was "TIME FOR CHANGE!"

Leaders in Europe have offered more measured responses. Several nations in the region have begun investing in Iran since sanctions were lifted following the 2015 nuclear deal.

French President Emmanuel Macron spoke with Rouhani and expressed concern over the violence and deaths in the past week.

He called for restraint, and the two leaders agreed to postpone the French foreign minister's visit to Tehran because of the current situation.

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Deadline looms

Trump has used the anti-government protests as an opportunity to slam the Iran nuclear deal ahead of key legal deadlines looming this month, actions that may foreshadow how he plans to proceed.

In mid-January, Trump will once again have to decide whether to certify Iran's compliance with the deal -- a process that must occur every 90 days according to the terms of the agreement.

He also faces perhaps an even more significant deadline over whether to renew temporary waivers for US sanctions against Iran.

The renewal of those waivers -- which provide relief for US sanctions not set to expire for several years -- must occur every 120 days to keep the United States a party to the deal and thus not violate the accord.

Iran's missile program is not in breach of its nuclear deal and will continue despite objections from the United States, Rouhani has said.