Supporters of jailed Ukrainian filmmaker Oleh Sentsov have marked the 100th day of his hunger strike with renewed calls on Russia to release him.

A vocal opponent of Russia's 2014 takeover of Ukraine's Crimean Peninsula, Sentsov was sentenced to 20 years in prison after being convicted by a Russian court in 2015 of conspiring to commit terrorist acts.

The 42-year-old has been on a hunger strike at a penal colony in Labytnangi in Russia's northern region of Yamalo-Nenets since May. He is demanding that Russia release 64 Ukrainian citizens that he considers political prisoners.

Russian authorities are reluctant to free Sentsov, despite reports of a dramatic decline in his health and pressure from Western governments and human rights groups, which have backed the film director's contention that the charges against him were politically motivated.

On August 21, several dozen people demonstrated in front of the Russian Embassy in Ukraine's capital, Kyiv, in support of the filmmaker.

Some of the participants carried signs reading, "Free Sentsov" and "Stop [Russian President Vladimir] Putin."

Meanwhile, Ukrainian Foreign Ministry spokeswoman Maryana Betsa tweeted that Kyiv demands Sentsov's immediate release.

"It is the 100th day of O. Sentsov's hunger strike. It is a scary number. Human life is the highest value. We demand that the Russian Federation immediately release Oleh," Betsa wrote.

Betsa also called on Ukraine's "partners and international organizations to increase pressure" on Moscow to release Sentsov and other Ukrainian political prisoners in Russia.

In Russia, 10 protesters were arrested by Russian police in an unsanctioned demonstration near Moscow's Griboyedov monument, according to OVD-Info, a human rights organization that monitors detentions.

The participants in the rally, who numbered more than 20, were holding Sentsov's portraits and posters calling for his release.

Elsewhere in Russia, activists from the Open Russia civic movement unfolded a big banner in the capital of the Tatarstan region, Kazan, saying, "Freedom for Sentsov, 100 days."

The banner was placed under the walls of the city's ancient fortress, known as the Kazan Kremlin.

In London, a group of demonstrators gathered outside Russia's Embassy, shouting, "Free Sentsov."

The PEN International association of writers, which organized the rally, planned to deliver "messages of support from all over the world" to the embassy and urge the Russian authorities to ensure that Sentsov is allowed to receive them in the penal colony where he is being incarcerated.

And in the Czech Republic, filmmakers said they were launching a rotating hunger strike in solidarity with their Ukrainian colleague, with seven of them participating in the first rotation.

"We'll be on hunger strike for five days, from this morning until August 25," Vit Janecek, a member of the Czech Association of Directors, Writers and Playwrights, told the AFP news agency.

"We're launching this initiative in the hope that other people will join during the next five-day cycles until the Sentsov case is resolved," he added.

And the French newspaper Le Monde carried a plea signed by dozens of figures from the world of culture also calling for Sentsov’s release, saying he "could die any minute."

Sentsov's cousin, Moscow-based journalist Natalya Kaplan, told the Associated Press news agency on August 21 that he was in intensive care in critical condition, adding that the family didn't have full information about his health.

After meeting with Sentsov at the penal colony on August 14, Zoya Svetova, a member of Russia's Presidential Advisory Council On Human Rights, told RFE/RL that the filmmaker was in "bad" health as a result of his hunger strike.

Russian human rights ombudswoman Tatyana Moskalkova said that the prison sent in a group of doctors to examine Sentsov on August 20 and they reportedly concluded that his condition was "satisfactory."

"He moves, gets up, and gets a special diet," Moskalkova added.

Russia's prison authorities had previously rejected claims about the filmmaker's worsening condition, saying that he's been given nutritional supplements.

Several governments, prominent figures, and Sentsov's family have called on Putin to pardon Sentsov, but the Kremlin said he would have to formally request a pardon himself before it could be considered.

Sentsov has said that he will not ask for a pardon because he believes he has not committed a crime.

He has also indicated that he is prepared to die of starvation to press his cause, vowing to continue the protest "to the end."

With reporting by AFP, AP, RFE/RL's Tatar-Bashkir Service, and RFE/RL's Russian Service