Ukrainian prisoner Oleh Sentsov, on hunger strike for the last 68 days, is on the edge of life and death, his cousin Natalya Kaplan has told The Independent.

“We don’t know how long his body will keep going, but we’ve been told he’s in a pre-death state,” she said. “It’s a miracle he has lasted this long.”

The filmmaker and pro-Ukrainian activist was detained in Crimea in 2014. A year later, he was controversially sentenced by military court to 20 years’ imprisonment.

The case against him was formally terrorism, but many believe the real reason was his active opposition to Russia’s annexation.

In May, he announced a hunger strike – the aim of which, he said, was not his own freedom, but that of several dozen Ukrainian political prisoners held in Russia. He told family and friends he was ready to go to the end.

Two weeks ago, Ms Kaplan travelled to the Russian far north, 2,000km away from Moscow, to see her cousin in prison. She said he had lost more than 15kg since beginning the hunger strike, and his health was “deteriorating rapidly”.

Approximately one week ago, Mr Sentsov was transferred to an intensive care unit following a heart seizure. No one is certain exactly when this happened, she said, since Mr Sentsov, in information isolation, is no longer sure of his calendar.

“He remembers that they tried to forcefeed him in hospital, but he resisted,” she said.

“They came up with a compromise, where he agreed to take two to three spoonfuls of nutritional mix to support his heart. After 68 days of starvation, he needs much more than this.”

Lawyer Dmitry Dinze, who visited Mr Sentsov on Thursday, described his client as in “very pale, very bad shape”. He likened him to the gaunt, haunted leading character in Kashchei the Immortal, a Soviet-era film.

But he told The Independent he had no doubt that Mr Sentsov would continue his hunger strike – even though he might have “just a few weeks” left.

We don’t know how long his body will keep going, but we’ve been told he’s in a pre-death state Natalya Kaplan, cousin

There is little sense that Ukraine and Russia are close to agreement on a deal that would see Mr Sentsov released. After a slow start, the Ukrainian government is doing “all that it can” to free him, Mr Dinze said.

Several prominent figures inside Russia and beyond have filed petitions, urging Vladimir Putin to pardon the film director.

On 22 June, his mother also wrote to the Russian president. “I will not try to persuade you about my son’s innocence, but I will simply say that he killed no one,” she wrote.

“His children are waiting for him. They will never be happy without a father.”

Kremlin spokesman Dmitry Peskov said he would look into the matter. But Mr Putin, who has insisted Mr Sentsov is a terrorist, has so far chosen not to respond directly.

Russia tests 'invincible' hypersonic missile

In June, Mr Putin reportedly agreed with Ukrainian president Petro Poroshenko that human rights ombudsmen would be allowed to visit prisoners in each others’ countries.

On 26 June, Russian ombudsman Tamara Moskalkova travelled to Kiev and was granted access to Russian sailors being held by Ukraine. Ukrainian ombudsman Lyudmila Denisova flew to Russia in return.

But she spent over two weeks trying, unsuccessfully, to get access to Mr Sentsov.

Ms Denisova told The Independent that she saw “no sign” the Russian side was ready to agree to release Mr Sentsov.

“We offered 36 people in exchange. We have not received one reply to our offer,” she said.