The arrests -- including that of Javad Emam, the spokesperson for the main reformist coalition -- came after Iranian and US officials held talks in Oman that both sides painted as positive.

On Saturday, Iran heaped more jail time on Nobel Peace Prize winner Narges Mohammadi, and on Monday arrested Hossein Karoubi, the son of prominent dissident Mehdi Karoubi.

Weeks after repressing a wave of protests, one of the greatest challenges to the government since it came to power in the 1979 Islamic revolution, Tehran has taken a two-track approach.

It is rounding up and jailing perceived critics, while at the same time pursuing a potential diplomatic opening with US President Donald Trump's administration.

A spokesperson for the Reformist Front coalition told local media on Monday that Iran's Revolutionary Guards had arrested the group's spokesman Emam.

Emam was one of at least five Reformist Front figures to be detained, as were several activists and filmmakers who co-signed a protest statement.

Iran's government has branded the protests "riots" fuelled by its arch-foes Israel and the United States.

- 'Frustrate the enemy' -

On Monday, supreme leader Ayatollah Ali Khamenei called on the nation to show "resolve" against foreign pressure.

"National power is less about missiles and aircraft and more about the will and resolve of the people," Khamenei said, adding: "Show it again and frustrate the enemy."

Alongside its defiant pronouncements, Iran has signalled it could come to some kind of deal to dial back its nuclear programme to avoid further conflict with Washington.

The official IRNA news agency reported that Iranian atomic agency chief Mohammad Eslami had said Tehran could dilute its highly-enriched uranium in return for sanctions relief.

"In response to a question about the possibility of diluting 60 percent enriched uranium," IRNA reported, Eslami "said this depends on whether all sanctions would be lifted in return".

The report did not specify whether such an agreement would include only nuclear sanctions imposed on Iran by the United States, or all international economic measures targeting the Islamic republic.

Diluting or "downblending" uranium means mixing it with other substances to reduce the enrichment level, so the final product does not exceed a given threshold -- thus extending the amount of time it would take Iran to create sufficient nuclear material for a bomb.

Tehran adamantly insists it has never planned to build a nuclear weapon and that enrichment for civilian research and energy is its sovereign right, but the US, Israel and most Western capitals do not believe this.

At the talks in Oman last week, the US and Iran agreed to discuss Tehran's nuclear programme, though Washington and Israel also want to put its ballistic missiles and support for regional militant groups on the agenda.

In separate calls with his Egyptian, Saudi and Turkish counterparts, Iranian Foreign Minister Abbas Araghchi "described the talks as a good start while emphasising the need to dispel mistrust about the American side's intentions and objectives", state television reported.

- Crackdown continues -

While Trump had initially threatened to intervene over Iran's repression of last month's protests, since the latest talks began, the United States has not given any sign that the crackdown on Tehran's domestic critics is a major concern.

On Saturday, Iranian Nobel Peace Prize winner Narges Mohammadi was sentenced to six years in prison on charges of harming national security.

She was also given a one-and-a-half year prison sentence for "propaganda" against Iran's Islamic system, her foundation said in a statement.

Already incarcerated for much of the past decade as a result of her campaigning against capital punishment and the mandatory dress code for women, she now faces up to 17 more years behind bars and 154 lashes.

The arrest of Reformist Front spokesman Emam followed those on Sunday of three other figures, including Azar Mansouri, who has led the coalition since 2023. Another reformist lawmaker was arrested on Monday.

The reformist camp largely backed incumbent president Masoud Pezeshkian in the 2024 presidential election.

Separately, Hussein Karoubi was also picked up. Karoubi's father Mehdi Karoubi was a figure in the 2009 Green movement protests and has been under house arrest more or less ever since.

The authorities in Iran have acknowledged that 3,117 people were killed during the protests, publishing a list of 2,986 names, most of whom they say were members of the security forces and innocent bystanders.

International organisations have put the toll far higher.

The US-based Human Rights Activists News Agency says it has verified 6,964 deaths, mostly protesters, and has another 11,730 cases under investigation.

It has also counted more than 51,000 arrests.