Hundreds of Ukrainians, including civilians and local politicians, are being subjected to forced detentions by Russian forces in occupied regions, the UN has told the BBC.

Officials said they had verified some 271 cases of forced detentions, with many of those seized facing torture.

Separately, a Ukrainian politician told the BBC that he was waterboarded after being abducted by the Russian military.

Russia's defence ministry did not reply to a request for comment on the claims.

Oleh Pylypenko, the elected head of the Shevchenkivska united territorial community in southern Ukraine, said he was seized by Russian paratroopers near Kherson on 10 March while delivering aid to constituents.

Warning: this article contains descriptions of torture

The 36-year-old told the BBC that he was arrested along with his driver at a roadblock by Russian troops and suspected he was deliberately targeted after sharing the locations of Russian artillery with Ukrainian forces.

"I think that they started hunting specifically for me almost from the very start of the war. I believe they were planning an ambush because they wanted to take me alive," he said.

He was subsequently taken to an airfield, where allegedly he was tortured for three days by Russian paratroopers.

"They didn't touch my driver," Mr Pylypenko recalled. "They were interrogating only me. They used physical violence, electric currents and poured cold water over me during freezing temperatures outside. I had frostbite on my feet, damaged ribs and internal organs."

The father of three added that paratroopers also beat him with a "rubber club" and kicked him until he passed out. He also alleged that he was repeatedly subjected to electric shocks by the Russian troops.

"On the third day of all this I was so badly beaten up that I unable to move [independently]. And I wouldn't have survived without my driver, who was helping me all the time," he said.

Mr Pylypenko said he later became the subject of a turf war between paratroopers - who wanted to execute him for his part in helping Ukrainian forces target their positions - and military police, who wanted him to use his position to help organise prisoner swaps.

"These two groups had had an internal conflict about who would be further dealing with this prisoner of war. Because the paratroopers had just wanted to destroy me," he said.

The military police officers eventually won the fight, and after arranging 11 rounds of prisoner exchanges, Mr Pylypenko was finally released on 10 June.

Oleh Pylypenko and his family

A spokesperson for the UN's Office of the High Commissioner on Human Rights (UNOHR), whose monitoring mission in Ukraine has been documenting the abductions, told the BBC that at least 65 local politicians had been detained by Russian forces since the invasion began on 24 February.

They added that UN monitors had "documented cases of torture and ill-treatment of civilians subjected to enforced disappearances", which they said had taken place in improvised and former official places of detention controlled by either "Russian armed forces" or "affiliated armed groups".

Complaints included "credible allegations of beatings, strangling, electrocution, sexual violence, positional torture, and threats of execution with firearms, threats of physical violence against relatives, and providing no or scarce food", said the UNOHR.

Russia targets remaining civilians in Mariupol

In the occupied port city of Mariupol, an adviser to the city's elected mayor told the BBC he had received reports that a civil servant was executed by Russian forces after spending time in detention.

Petro Andryushchenko said the man, who had been a director with the city's transport authority, was tried and sentenced to death by a Russian-backed court.

The BBC cannot independently verify the report, and the UN said while it had received "allegations of the killings of civilians in Mariupol outside of hostilities, allegedly perpetrated both by Russian armed forces and affiliated armed groups" in the city, it had not yet been able to corroborate them.

But Mr Andryushchenko affirmed that mass detentions were ongoing in the region and that around 10,000 people had been arrested by Russian forces.

Local politicians who "don't want to work with the regime" or representatives from "pro-Ukrainian parties" are among the most frequent targets, he said.

Former police officers, Red Cross volunteers and civilians who held pro-Ukrainian views were also being targeted in the city, he said, with many being sent to former Ukrainian prisons and makeshift "filtration" camps.

Moscow's search for collaborators

Dmytro Vasyliev, a former speaker of the local council in the occupied southern city of Nova Khakova, told the BBC that he was arrested by Russian proxy forces from the self-proclaimed Donetsk People's Republic in March.

Mr Vasyliev was held for 46 days before being released. During his detention he was repeatedly interrogated by balaclava-clad guards who pressured him to collaborate with the occupying force.

"I was called for questioning about six times," the 54-year-old said. "The questions were only about co-operation. 'Do you have links with the Ukrainian security services or military?' Then in the end they just suggested that I co-operate with them - to have a think."

He said beatings by prison guards were a regular feature of life for those held at the detention centre in a former police station in Nova Kakhova.

"I wasn't hit. Other people were - I heard it every day, but not me," he recalled. "I spoke to two people. One was an elderly man who was once an ambulance driver in the Donbas military operation zone. He was hit."

Another man in the cell next to him was "beaten badly during the first few days" of his detention, he added.

Mr Vasyliev said in most cases there was no reason or purpose behind the beatings. They were carried out "just because", he said.

On his final day in detention, he said the prison officials revealed to him they were officers with Russia's internal security service, the FSB.

Other Ukrainians abducted by Russian forces have similarly alleged the FSB was involved in their arrests.

In March, Viktoriia Roshchyna, a journalist with Ukrainian media outlet Hromadske, said she had been abducted and interrogated by FSB officers in the occupied city of Berdyansk.

A still from Viktoriia Roshchyna hostage video

The UN has told the BBC it has documented many cases of FSB officers taking part in the "detention, torture and ill-treatment" of Ukrainian civilians.

Both Oleh Pylypenko and Dmytro Vasilyev remain free, though Mr Pylypenko continues to work on the front line of the conflict delivering aid to his constituents.

But dozens of Ukrainian officials remain in custody.

In a short statement, Ukraine's ministry of defence called the detention and torture of local politicians "shameful" and said all allegations must be investigated urgently.

"Russia should bear the brunt of responsibility," it added.

Russia's defence ministry did not respond to requests for comment on the allegations. The Russian government has previously denied carrying out war crimes in Ukraine. Ukraine's prosecutor general has said her office is receiving 200-300 reports of war crimes a day but cannot investigate every case "properly and effectively" because of a lack of access. (BBC)

Update news