Civilians in Yemen have described torture at the hands of the Houthi rebels including being strung up by their genitals and doused in acid.

Their horrific testimonies emerged as tense peace talks in Sweden between the country’s warring factions entered a second day.

The gruesome accounts underscore the importance of a massive UN-backed prisoner swap that was signed on Thursday by the Iran-backed rebels and Yemen’s recognised government, who have been fighting since March 2015.

According to the deal, some 5,000 prisoners from both sides will be released as a confidence-building measure to bolster the peace negotiations, which kicked off north of Stockholm this week.

Since the start of the three-and-a-half-year civil war, more than 18,000 people are believed to have been locked up by the Houthi fighters and many of them tortured.

Torture has also been recorded by rights groups in prisons run by the Yemeni government and its Gulf allies, including the United Arab Emirates.

Farouk Baakar, a Yemeni medic at al-Rashid hospital in north Yemen, was arrested by seven militiamen in 2016 after treating a man who had been tortured and shot by the Houthis.

Mr Baakar told Associated Press (AP) he was held for 18 months in Houthi-controlled prisons, including in the “Pressure Room”, the basement of a 500-year-old Ottoman castle in the Red Sea city of Hodeidah. There he said he was stripped, whipped and his nails and hair were pulled out. He was later splashed with melted plastic, beaten and chained to a ceiling by his wrists for 50 days until his captors thought he was dead.

“It was so painful, especially when they come the next days and press on the bruises with their fingers,” he said.

Survivor Monir al-Sharqi was dumped in a stream, half-naked, emaciated and bearing horrific marks of torture after imprisoned by Houthis (Photos AP/Nariman El-Mofty)

The doctor described trying to treat other prisoners held with him who had been tortured, with makeshift tools such as electrical wire.

One man said he had been hung by his penis and testes and was unable to urinate. Another’s buttocks had been sealed after the Houthi guards doused his back with acid, melting his skin. Mr Baakar described using wire to help him make an opening and remove excrement.

“When I asked Houthi guards for help, saying the man is dying, their only answer was: ‘Let him die’,” Mr Baakar added.

The doctor was released last December after his family paid 5.5 million rials, about $8,000 at the time, and fled to Marib, an anti-Houthi stronghold in central Yemen where he now lives in a tent.

He is one of 23 people interviewed by AP who either survived or witnessed torture in Houthi detention centres.

The testimonies come just months after both Human Rights Watch and Amnesty International accused the UAE, and its allied Yemeni forces, of torturing detainees in their secret prisons in the south of Yemen.

In those prisons, the rights groups said people had been electrocuted, stripped, caned and whipped.

The UAE is part of a Saudi Arabia-led alliance that launched a bombing campaign in March 2015 to oust the Houthi rebels, who had swept control of the country, forcing recognised Yemeni president Abedrabbo Mansour Hadi to flee.

That triggered a nearly four-year war that has sparked the world’s worst humanitarian crisis in terms of numbers.

Yemeni medic Farouk Baakar demonstrates how he was shackled to a wall during his torture in a prison run by Yemen’s Houthi rebels (AP/Nariman El-Mofty) (AP Photo/Nariman El-Mofty)

The UN’s envoy to Yemen, Martin Griffiths, warned this week that half of the country’s 30 million population could be at risk of famine if the conflict does not end immediately.

As many as 16,000 civilians have been killed, according to the UN. On Friday it said at least 1,500 civilians were killed or injured between August and October alone: an average of 123 civilian casualties every week.

The UN hopes the peace talks in Stockholm will at least lead to a ceasefire to allow humanitarian aid groups to access the most devastated areas. They are the first talks since 2016.

The prisoner swap will see the release of detainees, people who have been forcibly disappeared and those under house arrest.

The International Red Cross said it would oversee the exchange, which is expected to take weeks.

When I asked Houthi guards for help, saying the man is dying, their only answer was: ‘Let him die’ Farouk Baakar

On Friday, Yemen’s recognised government proposed reopening the Houthi-held airport in the capital Sanaa on the condition that planes are first inspected in the airports of Aden or Sayun which are under its control. This would help alleviate the humanitarian suffering.

All sides have repeatedly denied allegations of torture in their detention centres.

In July, the UAE said it believed the accusations against it to be “politically motivated to undermine its efforts as part of the Arab coalition to support the Yemeni government”.

The Houthi human rights ministry meanwhile said in a statement in late 2016 that “there is no policy or systematic use of torture on prisoners”. It added that the ministry and prosecutors are working to “ensure the rights of prisoners and provide all legal guarantees to achieve justice and fair trials”.

But civilians and aid workers tell a different story.

The Abductees’ Mothers Union, an association of female relatives of detainees jailed by the Houthis, said that of the 18,000 prisoners they have documented, at least 1,000 were tortured in a network of secret prisons.

Sabah Mohammed, a representative of the group in the city of Marib which is now under government control, said at least 126 prisoners have died from torture since the Houthis took over Sanaa in late 2014.

Anas al-Sarrari sits in his wheelchair in his home in Marib, Yemen after he was left paralysed by torture in Houthi prisons. In prison, he was hung from the ceiling by his wrists almost non-stop for 60 days and severely beaten (AP/Nariman El-Mofty) (AP Photo/Nariman El-Mofty)

Anas al-Sarrari, 26, a critic of Houthi brutality, said he is now wheelchair-bound after being paralysed by the torture he suffered in a prison in Houthi-controlled capital Sanaa.

He told AP he was strung up for 23 hours a day until the handcuffs sliced his wrists. After being beaten with a stun gun, he could no longer use his legs. No one helped him get to the bathroom, so he was forced to urinate and defecate on himself until he was released.

“To see people with disabilities, coming out of prison after excessive torture will terrify everyone – ‘Look, this will happen to you if you speak up’,” he said.

Another former prisoner, Hussein, a teacher from the northern city of Dhamar, told AP he was held blindfolded in an underground cell for four months and 22 days. Throughout his confinement, he said, his jailers beat him with iron rods and told him he was going to die.

Monir al-Sharqi, a lab technician who disappeared for a year, meanwhile was tortured so badly he can no longer speak. His family believe he was tortured by the Houthis for his activism, after he was found dumped by the side of a river with horrific wounds.

Nurses change the dressings on the severe burns covering Monir al-Sharqi, at the Marib General Hospital in Yemen. His torture was so extreme he has lost his memory and can barely speak, mumbling unintelligibly when asked questions (AP/Nariman El-Mofty) (AP Photo/Nariman El-Mofty)

Meanwhile in southern Yemen, where the recognised government and its UAE backers are in control, former detainees told of their torture.

One prisoner, Adel al-Hassani, was held in Bir Ahmed prison in the southern port city of Aden. He told Channel Four this week that Emirati guards electrocuted him in his genital area while he was hung from the ceiling.

“When the night comes in the UAE prisons, you hear the screams everywhere,” said the former pro-government soldier who was arrested after he became critical of the Emirati intervention in Yemen.

He added: “Some guys are dangled or suspended. Others are electrocuted, and others stripped or kicked.”

He said he was also bound by his hands and legs, blindfolded and put in a narrow hole in the desert nicknamed the “monster hole”, for 48 hours where he nearly died.