A British-born environmentalist who was released on furlough with an electronic tag from Iran's notorious Evin prison in July has been sent back to the jail.
Morad Tahbaz, 66, was staying with his family in the capital Tehran when he was taken by Iranian authorities.
Mr Tahbaz's family tweeted: "Early this morning, Morad Tahbaz was taken back to Evin Prison after a temporary furlough.
"This was the 'deal' that [former British prime minister Liz Truss sold out Morad for, instead of bringing him home with the other hostages months ago.
"Rishi Sunak, you have the chance to right this wrong. Free Morad."
UK Foreign Office minister Lord Tariq Ahmad also called for Mr Tahbaz's release.
“The Tahbaz family have confirmed that Morad has been returned to Evin prison by the Iranian authorities," he said.
"By continuing his horrendous ordeal with these cruel tactics, Iran sends a clear message to the international community that Iran does not deliver on its commitments.
“We call on Iran to release Morad so he may rejoin family in Tehran immediately.
"We will continue to work closely with our US partners to hold Iran to account, and to secure Morad’s permanent release and departure from Iran.”
Daughter of Morad Tahbaz stages protest in London - in pictures
In March, the UK said it had secured Mr Tahbaz’s furlough, along with the release and return of British Iranians Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori.
This came after the UK government finally agreed to settle a £400 million ($465m) debt to Iran dating back to the rule of the Shah in the 1970s.
But two days later, Mr Tahbaz was forced to return to Evin prison.
In July, Mr Tahbaz was allowed medical care on another temporary furlough with his family in Tehran on the condition that he wore an ankle bracelet.
It is understood that then foreign secretary Liz Truss told Mr Tahbaz’s family that the UK could not secure his full departure from Iran because he is also an American citizen, and Iranian authorities were having discussions with the US.
On Wednesday, Ms Zaghari-Ratcliffe said she would continue to speak up Mr Tahbaz and other detainees.
"My story is the story of many people in Iran who remain in prison. I've got the responsibility to be their voice," she said.
Rishi Sunak through the years - in pictures
Mr Tahbaz, a prominent conservationist and board member of the Persian Wildlife Heritage Foundation, was arrested during a crackdown on environmental activists in January 2018.
The British-Iranian national was sentenced to 10 years in prison with his colleagues on vague charges of spying for the US and undermining Iran’s security.
His wife has also been placed under a travel ban by Iranian authorities.
Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori released – in pictures
Amnesty International urged Foreign Secretary James Cleverly to increase pressure on the Iranian authorities for Mr Tahbaz’s release, and meet with his family.
“This is, of course, terrible news for Morad and a very distressing development for his family," said Sacha Deshmukh, the charity’s UK chief executive.
“Morad is a conservationist who should never have been jailed in the first place, and we want to see the foreign secretary stepping up pressure on the Iranian authorities to secure his immediate and unconditional release, and his return to the UK along with his wife Vida.
“The foreign secretary must urgently meet with the family to outline the UK’s plans to secure Morad’s freedom, while pushing hard for full and unfettered consular access while Morad remains in detention.”
Nazanin Zaghari-Ratcliffe speaks for first time since release from Iran - video
Nazanin Zaghari-Ratcliffe speaks for first time since release from Iran
This latest development in his case follows the US imposing new sanctions on Iranian officials, including the head of Evin prison and Islamic Revolutionary Guard Corps commanders, over Tehran's "brutal ongoing crackdown" of protests, the Treasury announced.
US Secretary of State Antony Blinken said the latestsanctions were imposed 40 days after the death of Mahsa Amini, 22, who died while in custody of Iran's "so-called morality police".
The US has blamed Iran's morality police for the death of Amini, who was taken into custody in Tehran on September 13 for wearing her headscarf too loosely.
Amini, of Kurdish origin, died three days later.
The Treasury imposed sanctions on 10 people, including two senior IRGC leaders and provincial officials from Sistan and Baluchestan province, which has seen some of the deadliest violence against protesters since demonstrations began last month.
Amini's death has sparked protests that have involved women taking off their veils, with crowds calling for the downfall of Iranian supreme leader Ayatollah Ali Khamenei.
Thousands have been detained by security forces and more than 200 killed, including children, rights groups said.
On Wednesday, Ms Zaghari-Ratcliffe spoke out about the protests in Iran, saying they had reached a point of "no return" as demonstrators demand wide reforms.
She spent six years detained in Iran until she was freed in March after successful negotiations between the British and Iranian governments.
She was visiting her parents in Iran when she was arrested in 2016 and separated from her daughter.
On Wednesday, Ms Zaghari-Ratcliffe gave a speech to the Thomson Reuters Foundation's charity Trust Conference and criticised the situation in Iran.
She said the government's suppression of the demonstrations and shutting down of the internet showed the regime was scared of losing control.
"The anger has been building up for many, many years," Ms Zaghari-Ratcliffe said.
"We can see a coming together for one single goal and that is freedom. The protests are really, really powerful this time. I don't think we've ever seen the unity we're seeing now."
She described Amini's death as the "spark for an explosion".
"There is a generational shift which plays a massive role in the new movement," said Ms Zaghari-Ratcliffe, who works for the foundation as a project manager.
"This is the generation of social media and TikTok and the internet. They know more about the world and their rights than we did. They have a lot more courage than we did."
'Is that mummy?' Emotional scenes as Nazanin and Anoosheh are reunited with their families - video
'Is that mummy?' Emotional scenes as Nazanin and Anoosheh are reunited with their families
On Tuesday, the UK announced it was considering taking “very strong action” against Iran after a clampdown by Tehran's security forces that included firing live ammunition and bird shot at protesters, the British Parliament was told on Tuesday.
MPs urged the government to impose sanctions on the Islamic Revolutionary Guard Corps and press for a UN investigation into alleged human rights abuse.
Iranian security forces were filmed firing tear gas during a raid on a girl’s school in Tehran on Monday, with many videos of the incident being posted on social media.
Ministers will also investigate claims that family members of Iran’s leaders are applying for British passports to seek refuge in London.
Thousands defy Iranian police to mourn Mahsa Amini - video
Thousands defy Iranian police to mourn Mahsa Amini
The UK is looking “at all options to hold Iran to account”, MPs were told, as they held a debate over the protests.
“The Iranian regime’s use of live ammunition and birdshot against protesters is barbaric,” Foreign Office minister Gillian Keegan told the Commons.
Ms Keegan accused the regime in Tehran of having a “flagrant disregard for human rights”.
“We condemn the Iranian authorities," she said. "Obviously we’ve taken very strong action.
“We condemn the crackdown on protesters, journalists and internet freedom, and the use of violence in response to the expression of fundamental rights by women or any other members of Iranian society is wholly unjustifiable.
“We will continue to work, including with our international partners, to explore all options for addressing Iran’s human rights violations."
Iran protests 40 days since Masha Amini's death - in pictures
Iran imposed sanctions on British institutions and people last week after the UK blacklisted Iran's morality police amid protests over the death of Amini.
Britain's National Cyber Security Centre and the Government Communications Headquarters, known as the GCHQ, were among seven institutions listed.
Conservative MP Bob Stewart said he had heard “substantial rumours” that Iranian elites were trying to make London “a place of safe refuge” and were applying for British passports.
Ms Keegan said in response: "Obviously we have our own rule of law here in the UK but in relation to the rumours he has heard about passports, I haven’t heard those but I will certainly look into that.”
