The activist, Vitaly Shishov, went missing Monday after going out for a morning jog, said his colleagues, who accused the Belarusian authorities of killing him. Kyiv police said that Shishov had been found hanged in the park and that their investigation was considering the possibility that the death was a “murder masked as a suicide.”

“The full picture of events will be confirmed after the questioning of witnesses, the analysis of video recordings” and other investigative steps, the police said.

Alexander Lukashenko, Belarus’ authoritarian leader, who has been in power since 1994, has long repressed dissent at home and jailed thousands after large-scale protests over his rule last year. Now, events in recent weeks suggest that he is also escalating his campaign against the growing number of Belarusian exiles abroad.

In May, Lukashenko forced the landing of a passenger plane with an exiled Belarusian activist aboard and had him arrested. On Sunday, a Belarusian Olympic sprinter sought protection at a Tokyo airport as her nation tried to forcibly send her home from the Summer Games. She said she feared for her safety after criticizing her coaches and the country’s national Olympic committee.

Shishov was the director of the Belarusian House in Ukraine, an organization that helped people trying to escape repression in Belarus after the anti-government protests last summer and fall. He was 26, according to local news reports.

While the circumstances surrounding Shishov’s death remained murky, critics of Lukashenko quickly pointed the finger at his authoritarian regime.

“It is worrying that those who flee Belarus still can’t be safe,” Svetlana Tikhanovskaya, the pro-democracy opposition leader from Belarus who fled the country last year after claiming victory in a presidential election, said on Twitter.

Shishov disappeared after going out for a 9 a.m. jog near his Kyiv home Monday, colleagues at Belarusian House said in a statement. Since fleeing to Ukraine last fall, the statement said, he had organised aid for other exiles, staged anti-Lukashenko protests and petitioned Ukrainian authorities to support the Belarusian diaspora.

“The death takes place amid an unacceptable Belarusian crack down on civil society,” the US Embassy in Kyiv said on Twitter. “We look forward to a complete and thorough investigation by Ukrainian authorities to establish its causes and circumstances.”

Last week, according to his Facebook posts, Shishov helped organize a rally in Kyiv marking the 31st anniversary of Belarus’ independence from the Soviet Union.

His colleagues said that he believed he was being followed and that supporters in Belarus had warned him of potential threats to his life. He responded jokingly that if something happened to him, it might help his organization get much-needed attention.

“Vitaly faced these warnings with stoicism and with humor,” the organisation said. “There is no doubt that this was a spy-organized operation to liquidate a Belarusian who was truly a danger to the regime.”

Shishov, from the Belarusian city of Gomel near the Ukrainian and Russian border, arrived in Kyiv after taking part in anti-government rallies, his colleagues said. Last year’s protests erupted after Lukashenko claimed a landslide victory in a presidential election that was widely considered fraudulent.

For many exiles, Ukraine, which has a visa-free policy for Belarusians, is a transit point on the way to European Union countries like Poland and Lithuania. But Shishov decided to stay and became part of Kyiv’s growing community of Belarusian activists. He participated in solidarity rallies at Kyiv’s central Independence Square and tried to help other new arrivals find work and lodging.

“He was a calm, balanced person,” said Alena Talstaya, a leader of Razam, another Belarusian opposition group in Kyiv. “He said his main sphere of activity was helping refugees.”

The flow of Belarusian exiles to Ukraine increased in recent weeks, Talstaya said, amid a wave of raids and arrests directed against journalists and rights activists. Lukashenko said last month that his security services were mounting a “cleansing operation” against Western-backed “bandits and foreign agents” intent on unseating him.

As a result, hostels, hotels and friends’ spare rooms in Ukraine filled with Belarusians fleeing possible arrest, Talstaya said. Even abroad, however, Belarusians are not completely safe.

“Hiding is impossible and pointless,” Talstaya said. “No person can live in permanent fear.”

© 2021 The New York Times Company