US President Donald Trump threatened on Friday to come to the aid of protesters in Iran if security forces fire on them, days into unrest that has left several dead and posed the biggest internal threat to Iranian authorities in years.

"We are locked and loaded and ready to go," he said in a social media post. The United States struck Iranian nuclear facilities in June, joining an Israeli air campaign that targeted Tehran's atomic programme and military leadership.

Top Iranian official Ali Larijani responded to Trump's comments warning that US interference in domestic Iranian issues would equal the destabilisation of the whole region. Iran backs groups in Lebanon, Iraq and Yemen.

The comments came as a local official in western Iran where several deaths were reported was cited by state media as warning that any unrest or illegal gatherings would be met "decisively and without leniency", raising the likelihood of escalation.

Biggest protests in three years

This week's protests over soaring inflation have spread across Iran, with deadly confrontations between demonstrators and security forces focused in the western provinces of Lorestan and Chaharmahal and Bakhtiari.

State-affiliated media and rights groups have reported at least six deaths since Wednesday, including one man who authorities said was a member of the Basij paramilitary affiliated with the Revolutionary Guards.

Iran has seen off repeated bouts of major unrest in recent decades, often quelling protests with heavy security measures and mass arrests. But economic problems may leave authorities more vulnerable now.

This week's protests are the biggest in three years, since nationwide demonstrations triggered by the death of a young woman in custody in late 2022 paralysed Iran for weeks, with rights groups reporting hundreds killed.

Also Read: Several reported killed in Iran protests over economic woes

During the latest unrest, the elected President Masoud Pezeshkian has struck a conciliatory tone, pledging dialogue with protest leaders over the cost-of-living crisis, even as rights groups said security forces had fired on demonstrators.

Speaking on Thursday, before Trump threatened US action, Pezeshkian acknowledged that failings by the authorities were behind the crisis.

"We are to blame... Do not look for America or anyone else to blame. We must serve properly so that people are satisfied with us.... It is us who have to find a solution to these problems," he said.

Pezeshkian's government is attempting a programme of economic liberalisation, but one of its measures, deregulating some currency exchange, has contributed to a sharp decline in the value of Iran's rial on the unofficial market.

The sliding currency has compounded inflation, which has hovered above 36% since March even by official estimates, in an economy battered by Western sanctions over Iran's nuclear programme.

The Israeli and U.S. strikes last year have added to the pressure on the authorities, as have the ousting of Syria's Bashar al-Assad, a close Tehran ally, and the Israeli pounding of its main regional partner, Lebanon's Hezbollah.

Iran continues to back groups in Iraq that have previously fired rockets at US forces in the country, as well as the Houthi group that controls much of northern Yemen.

"American people should know that Trump started the adventurism. They ought to watch over their soldiers," said Larijani, the head of Iran's National Security Council and a top adviser to Supreme Leader Ayatollah Ali Khamenei.

Killings, arrests

The Hengaw human rights group reported on Thursday that 29 protesters had been detained during the latest wave of demonstrations, including 14 ethnic Kurds, seven Lors, seven women, and two children.

In Lorestan Province, home to much of Iran's Lor ethnic population and site of some intense protests, a senior judicial official told state media: "There will be no tolerance for illegal actions that threaten public order and safety."

The media said law enforcement forces had identified and arrested several "disruptive individuals" in the Lorestan counties of Azna and Delfan.

Chaharmahal and Bakhtiari has also witnessed protests.

The semi-official Fars News Agency reported on Thursday that three protesters were killed and 17 were injured during an attack on a police station in western Lorestan.

Fars and Hengaw also reported fatalities in Lordegan in Chaharmahal and Bakhtiari province. Authorities confirmed one death in Kuhdasht, Lorestan, while Hengaw reported another in the central province of Isfahan.