The son of a British couple detained by the Taliban five months ago has told the BBC that he fears they may die in prison.

Peter Reynolds, 80, and Barbie, 76, were arrested on 1 February while returning to their home in central Bamiyan province, Afghanistan. It is not known exactly why they were detained.

Their son Jonathan Reynolds said their health was rapidly deteriorating, with his father suffering serious convulsions and his mother "numb" from anaemia and malnutrition.

The Taliban's foreign minister said they were receiving medical care and that "efforts are under way to secure their release, but the process is not complete".

"All their human rights are being respected," Amir Khan Muttaqi told reporters in Kabul on Wednesday, adding that the pair had "occasional contact" with family.

The UN warned on Monday that the couple could perish "in such degrading conditions" if they do not receive medical care at once, calling their detention "inhumane".

Mr Reynolds said it had been a "harrowing and surreal" five months waiting for the release of his parents, who lived in Afghanistan for 18 years, where they had citizenship and ran education projects.

One of these projects involved training women and children and had apparently been approved by local authorities, despite the Taliban banning education for girls over 12-years-old and not allowing women to work.

Mr Reynolds said his parents had been held in harsh conditions - including a maximum security prison - despite being "deemed innocent" by a judge and facing no charges.

"My dad was chained to murderers and criminals," he told BBC Radio 4's Today programme, adding that they had at one point been held in a basement for six weeks without sunlight, and not allowed out.

The couple revealed "just how bad their health is" when they last had contact with their children on 15 June, Mr Reynolds said.

"My dad's health is deteriorating fast in particular," he said of the 80-year-old, who has a history of minor heart attacks.

"Now he's maybe got something like early Parkinson's - tremors and shakes down the right side of his body, his arms and face," he told BBC Breakfast.

He added that his father spent "half an hour convulsing on the prison floor" before his wife called for a prison guard to move him onto a "mattress pad on the floor" serving as a bed.

Mrs Reynolds "has blue hands and feet to do with anaemia, malnutrition, just not getting the right healthcare," he added.

Mr Reynolds said he did not know his parents' exact location - and that he was unsure "that the demand has been made for their immediate release".

He said he was very grateful that British officials visited the pair just last week and shared a photo with the family as "proof of life". It remained "frustrating", however, that this stopped short of securing their release.

"Every week it seems like we're told 'just wait two or three more days now… just hang tight'.

"Week after week we're told that - and they're still in prison."

However, he said he was grateful to the Foreign Office (FCDO) for the level of communication with the family.

The couple have both had birthdays in prison, and last week marked their 55th wedding anniversary; they married in Kabul in 1970.

Mr Reynolds said: "I'm thankful they were together, but they're certainly not free."

The UN likewise warned on Monday that the pair's health was quickly declining, and questioned why they were being held at all.

"Without access to adequate medical care, they are at risk of irreparable harm or even death," read a statement by the UN's human rights body, which called for their immediate transfer to a civilian hospital.

"We see no reason why this older couple should be detained at all, and have requested an immediate review of the grounds of their detention.

"It is inhumane to keep them locked up in such degrading conditions and more worrying when their health is so fragile."

It added that it had raised the couple's case with the Taliban and the UK.

An FCDO spokesperson said: "We are supporting the family of two British nationals who are detained in Afghanistan."

The UK shut its embassy in Kabul and withdrew its diplomats from the country after the Taliban returned to power in 2021.

The FCDO says support for British nationals in Afghanistan is therefore "severely limited" and advises against all travel to the country.