BEIRUT — Iran's Supreme Leader Ayatollah Ali Khamenei delivered a defiant speech on Friday, excoriating protesters as "saboteurs" and insisting the Islamic Republic would "not back down," even as the country remains in the throes of a full communications blackout amid growing antigovernment demonstrations.

Speaking before a crowd that periodically broke into chants of "Death to America," Khamenei accused protesters of working on President Donald Trump's behalf, saying they were acting "as mercenaries for foreigners."

"Last night in Tehran, a bunch of vandals came and destroyed buildings that belonged to them to please the U.S. president," he said, adding that Trump's hands were "stained with the blood of thousands of Iranians."

In recent days, Trump has vowed to strike Iran's leadership if government personnel kill protesters, a threat he repeated once again in an interview with Fox News late Thursday.

"If they do that, they're going to have to pay hell," Trump said, adding that the "enthusiasm to overturn that regime is incredible."

Khamenei said Trump's statements "emboldened rioters and elements hostile to the nation," and that Trump would be "overthrown."

"Were [Trump] truly capable of governing his own country," Khamenei said, "he would have attended to its numerous internal crises."

The unrest began a few weeks ago, with merchants and shopkeepers protesting the sharply falling value of the local currency, the rial.

Protests have since spread to all of the country's 31 provinces amid widespread anger against what many view as the government's corruption and mismanagement of the economy. According to the Norway-based NGO Iran Human Rights, at least 51 protesters have been killed since the protests began in late December.

Khamenei's belligerent address followed a tense Thursday evening, as demonstrations surged across the country's major cities, according to rights groups, apparently answering the call to protest from exiled Crown Prince Reza Pahlavi, whose father, the shah, was ejected in the 1979 Iranian revolution.

Video broadcast by the semiofficial Tasnim News Agency depicted burning buildings and scenes of destruction that were said to have been perpetrated by "terrorists." Other state-affiliated media showed vehicles, including cars and motorcycles, set on fire, along with damage to metro stations.

A resident in central Tehran sent recordings of a crowd in a street near their home shouting slogans in support of Pahlavi and "death to the dictator."

"Pahlavi returns. Death to Khamenei!" people chanted. Soon after that message was received, the country was plunged into an internet blackout, according to internet monitor Netblocks.

Though the cause of the blackout was unclear, Netblocks said it followed "escalating digital censorship measures" by the government against the protests.

Previous rounds of popular unrest have also seen the government shut down communications, usually as a prelude to an all-out crackdown.

Netblocks confirmed early Friday the internet blackout persisted in Iran for more than 12 hours. Calls on landlines to people in Iran also failed to connect. Meanwhile, airlines in Turkey and the United Arab Emirates canceled flights to and from Tehran and other cities, airline websites show.

Pahlavi, a divisive figure in the Iranian opposition, has for years lobbied the U.S. to bring about regime change in his home country and reinstall the monarchy with him as its leader. On Friday, he issued another video address on the platform X, exhorting more people to join the protests so as to undercut the "regime's power of repression."

"Be assured that victory is yours," he said.

The protests are the largest antigovernment actions since nationwide demonstrations in 2022 following the death in police custody of 22-year-old Mahsa Amini, an Iranian Kurdish woman, but that have yet to equal their scale.

The Human Rights Activists News Agency, a group based in the U.S. but which relies on activists in Iran, reported a spike in arrests as authorities try to quell popular anger.

The government's rhetoric has bounced between placatory and enraged; condemning "rioters" while at the same time acknowledging the criticism as legitimate — perhaps one reason why observers say authorities have yet to deploy full force against demonstrators.

But that posture may have already changed. Earlier this week, Iran's Defense Council, a body created after the 12-day war with Israel and the U.S. last June, vowed to take tougher measures against protesters. It was a line echoed by Khamenei on Friday.

"Everyone should know that the Islamic Republic, which came to power with the blood of several hundred thousand honorable people, will not back down in the face of those who destroy the Islamic Republic," he said. "It does not tolerate mercenary foreigners."

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