KYIV, Ukraine — A prominent activist who helped his fellow Belarusians seek refuge in Ukraine has been found dead in a Kyiv park near his home, Ukrainian police said Tuesday, leaving others who are self-exiled fearful that even countries considered havens are no longer safe from Belarus's strongman, Alexander Lukashenko.

Vitaly Shishov, the 26-year-old who led the Belarusian House in Ukraine that helps people fleeing from Belarus to settle abroad, was reported missing by his partner on Aug. 2 after he did not return from his morning run.

Kyiv police said Tuesday he was found hanged. They have launched an investigation into whether it was suicide or “murder disguised as suicide,” they said.

European Parliament President David Sassoli said on Twitter that “the fact Belarusian activists are being targeted in third countries is a serious escalation.”

In the past year, facing the greatest opposition challenge to his 27-year reign, Lukashenko has brutally cracked down on any dissent in Belarus, arresting thousands. The repression has sparked an exodus, with many Belarusians leaving the country for its Baltic neighbors Poland and Lithuania. Ukraine is considered another sanctuary — Belarusians are the second-largest minority there after Russians.

Ukrainian police are treating the death of Belarusian activist Vitaly Shishov as a suspected murder, after he was found hanged in a Kyiv park on Aug. 3. (Reuters)

It is still unclear whether Lukashenko’s regime is connected to Shishov’s death. But in recent months, Lukashenko has grown more aggressive in his campaign against critics abroad.

In May, Lukashenko brazenly ordered a MiG-29 fighter jet to force a civilian plane to land as it was flying over Belarus from Athens to Vilnius, Lithuania. Belarusian authorities then arrested one of its passengers, Roman Protasevich, the founder of an opposition media outlet.

Belarus has also upped the number of flights traveling to and from Iraq and sub-Saharan Africa as Lithuania has recently seen a huge spike in the number of people from those countries unlawfully crossing its border with Belarus. Lithuanian and European Union officials have said the sudden migration crisis isn’t organic, but Lukashenko’s audacious response to E.U. sanctions.

And on Sunday, in what became an international scandal on the world’s biggest sports stage, a Belarusian sprinter at the Olympics, Krystsina Tsimanouskaya, issued a public plea for help Sunday because she feared for her safety after criticizing the Belarus Olympic Committee.

Tsimanouskaya said Belarusian officials were pressuring her to board a flight back to Minsk against her wishes. She asked Japanese police for protection at Haneda Airport in Tokyo. On Monday, she received a humanitarian visa from Poland.

Although Ukraine has been a popular landing spot for many Belarusian and Russian dissidents in recent years, others question whether it is safe from state security agents who all used to be under one Soviet umbrella. In the past five years, two Russians critical of the Kremlin have been killed in Kyiv: former lawmaker Denis Voronenkov in 2017 and investigative journalist Pavel Sheremet in 2016. In both cases, Ukraine’s government alleged Russian involvement among its versions of what happened.

Christo Grozev of the investigative website Bellingcat, which specializes in combing through “open-source” digital data, told Echo of Moscow radio on Tuesday that he and his colleagues will now be directing all of their resources to investigate Shishov’s death.

In recent days, Bellingcat had found evidence of Russian state security agents infiltrating Belarusian diaspora groups in Kyiv, Grozev said.

Aliaksei Frantskevich, head of the Belarus Crisis Center in Lviv, Ukraine, said he suspects Shishov’s death could be “some kind of instrument of intimidation” for other Belarusian activists in exile.

Frantskevich said Shishov’s colleagues told him Monday that the activist recently described being surveilled.

“They’re doing this [intimidation and crackdown] in Belarus in a directed manner, and now they’ve moved on to neighboring countries,” Frantskevich said. “Ukraine is next door, there’s visa-free travel and a large number of Belarusians, and some are more radically inclined.”

Alena Talstaya, co-founder of Movement of Solidarity “Together” in Kyiv, which works with Belarusian refugees, said Shishov’s colleagues conducted searches until late Monday evening at the park where Shishov’s body was found Tuesday morning.

“We know that the intelligence services work not only on Ukrainian territory, but on the territory of European countries,” she said. “Whom it was done with or with whose help, we can only guess.”

Khurshudyan reported from Moscow. Mary Ilyushina in Moscow contributed to this report.