Men in Tehran look at newspapers reporting on the talks between Iran and the US that began on Friday © AFP via Getty Images

Iran’s security forces have arrested at least four senior reformist politicians on suspicion of plotting to overthrow the Islamic system, increasing tensions just weeks after the country’s deadliest unrest for years.

The arrests were made at a time of strained relations with the US, which began talks with Iran on Friday, but is still weighing its potential military options against the Islamic republic.

The state-affiliated Fars news agency reported that Azar Mansouri, head of the Reformist Front — an umbrella organisation representing reformist parties — was arrested at her home on Sunday. Mohsen Aminzadeh, a former deputy foreign minister for American affairs, and Ebrahim Asgharzadeh, a veteran politician, were also detained.

The identity of the fourth detainee was not disclosed. State media said some other senior figures had also been summoned to the judiciary.

Fars accused those detained of “targeting national solidarity”, opposing the constitution, co-ordinating with “the enemy’s propaganda” and encouraging “surrender” while establishing “secret mechanisms to overthrow” the Islamic theocracy. Three other prominent anti-regime political activists who have called for a constitutional referendum have also been detained over the past week.

Iran is facing mounting domestic and diplomatic pressure over the unprecedented death toll from the recent street protests and the growing risk of military confrontation with Washington. US President Donald Trump said the US had “very good” talks with Iran on Friday and that negotiations would continue, but warned that the consequences for Tehran would be “very steep” if the sides did not reach a deal.

The Human Rights Activists News Agency has put the number of people killed during last month’s protests at 6,842. The Iranian government has confirmed 3,117 deaths, including members of the security forces, but blamed the violence on what it says were US- and Israel-backed mercenaries and “terrorists”.

Iranian opposition groups abroad claim the death toll runs into the tens of thousands. Western diplomats are examining those estimates but acknowledge it is very difficult to know how many exactly were killed because of limited access to information.

The deaths have shaken Iranian society and prompted reformist politicians to speak out and demand accountability for the crackdown.

Recent Instagram posts by Mansouri reflected deep disillusionment with the possibility of reform within Iran’s existing political structure. She expressed regret over backing Masoud Pezeshkian’s presidential campaign two years ago and called on him to resign.

Mizan, a news agency affiliated with Iran’s powerful judiciary, reported that those arrested on Sunday had engaged in “co-ordinated activities aimed at inflaming the country’s political and social climate amid military threats from the US and Israel”.

Meanwhile, Ali Shakouri-Rad, a senior politician and former reformist MP, has alleged in a leaked audio recording that security forces themselves carried out acts of sabotage during the protests to justify a bloody crackdown, and questioned official claims that foreign agents were responsible for the killings.

Amir-Hossein Sabeti, a hardline lawmaker, said on Sunday that Shakouri-Rad must present evidence for his claims or face trial.

The US stepped up its military presence in Gulf waters south of Iran before the two countries began talks that are expected to continue in the coming days.

According to diplomats and analysts, the White House has demanded that Tehran permanently end all uranium enrichment, accept limits on its ballistic missile programme and halt support for regional militant groups. Tehran has said it can accept limitations only to its nuclear programme.

Abbas Araghchi, Iran’s foreign minister and chief negotiator, said on Sunday that the country could not accept all US demands. He also stressed that the Islamic republic would not give up its right to enrich uranium domestically.

“Standing firm is our greatest challenge at the moment and the responsibility for that rests with the military and the diplomacy apparatus,” he said. “If you take one step back, it is unclear how far back you will have to retreat.”

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