The Ukrainian film director is on day 89 of a hunger strike. He was sentenced by a Russian court to 20 years in prison for "terrorist attacks" in Crimea.
President Emmanuel Macron will speak with Russian leader Vladimir Putin on Friday about jailed Ukrainian film director Oleg Sentsov, who has been on hunger strike since May and is gravely ill, a source in his Elysee office said.
Sentsov, imprisoned on what he says are political charges, began his hunger strike ahead of the World Cup to highlight Russia's human rights record.
The Crimea-born Sentsov, sentenced by a Russian court to 20 years in a high security penal colony in 2015 for "terrorist attacks" on the peninsula, is on the 89th day of a hunger strike.
Sentsov was accused of setting fire to two office buildings in Crimea, including one of Russia's ruling party, and of plotting to blow up a monument to Soviet state founder Vladimir Lenin.
He was charged with organising a "terrorist group" in Crimea aiming to wrest the peninsula back from Moscow's control.
Russia annexed Crimea in 2014.
The film director has denounced the trial as politically motivated, amid high tension between Russia and the West over the annexation.
Mother asks Kremlin to pardon son
Sentsov's mother Ludmila wrote to Putin on June 22, asking him to pardon Sentsov.
"I ask you ... not to ruin his life," the letter, published by the Echo of Moscow radio station, said.
"He has now spent four years in prison. His children are waiting for him, and his youngest son has autism. They are struggling without him," she wrote.
On Thursday, Kremlin spokesman Dmitry Peskov confirmed the letter was received.
A commission must now be set up to gather reports on Sentsov's health, behaviour and mental state, a journalist from the Novaya Gazeta newspaper cited Sentsov's lawyer as saying.
The commission will then assess whether he presents a danger to society and will make a recommendation for Putin to review, the lawyer, Dmitry Dinze, was cited as saying.
'The end is near'
Sentsov's health is rapidly declining, his lawyer and a relative said.
"Things are not just bad, they're catastrophically bad," Sentsov's cousin, Natalya Kaplan, wrote on social media on Wednesday.
"He can barely get up. He writes that the end is near, and he's not referring to when he will be freed," Kaplan said.
Speaking to Ukrainian newspaper Hromadske on Tuesday, Sentsov's lawyer said the filmmaker's heartbeat had slowed to 40 beats per minute and he was suffering from anaemia.
Amnesty International said it had requested access to visit Sentsov together with medical experts, but was denied.
"The Federal Correctional Service told us that his health is stable and they see no changes for the worse. But that information is two weeks' old. Sadly, we know as little as everyone else," Amnesty's Aleksander Artemev said.