Vitali Shishov led a group helping Belarusians flee repression in the country and went missing while jogging on Monday.
The Belarusian House in Ukraine, an NGO that helps people who have fled repression in Belarus, accused Minsk of a "planned operation" after its director Vitali Shishov was found dead in Kyiv on Tuesday.
"There is no doubt that this is a planned operation of the security forces to liquidate a person truly dangerous for the Belarusian regime," the group said on Telegram.
“Vitali was under surveillance and [Ukrainian] police were notified. We had been warned on several occasions, both by local sources and by people in Belarus of the possibility of all kinds of provocations up to and including 'kidnapping and liquidation,'" the NGO went on.
Shishov, 26, was forced to flee to Ukraine last fall after taking part in anti-government protests in Gomel, southern Belarus, and "actively opposing" authorities, the Belarusian House said.
"Vitaly was part of a large and growing community of political exiles in Ukraine, there are probably a few hundred very active in Kyiv alone," said Peter Zalmayev, Director of Eurasia Democracy Initiative, in an interview with Euronews.
"There are estimates that the number of Belarusians who have fled to Ukraine over political repression is 3,000 - 5,000," he added.
Zalmayev had met Shishov last week and was planning to have him on the weekly TV programme he hosts in Ukraine on Thursday.
Ukrainian police opened a murder investigation after Shishov was found hanged in one of Kyiv's parks on Tuesday, not far from his place of residence.
He had gone missing on Monday while out jogging, his organisation said on Telegram. Police said in a statement that his mobile phone and personal belongings had been removed from the scene.
Human rights group Viasna, citing friends of the activist, said on Telegram that Shishov had previously been followed by "unknown people" while jogging recently.
"He had a jogging routine everyday and so it was easy to learn his movements," Zalmayev told Euronews.
Police and volunteers had been searching the area where Shishov was last seen jogging with a team of dogs, the Belarusian House had said.
Kyiv confirmed that they had opened an investigation into "premeditated murder" and have not ruled out his the activist's death could have been a "murder disguised as suicide".
Police are appealing for witnesses and potential CCTV footage from the local area as part of the investigation.
However, Zalmayev was not optimistic that the investigation would lead to a conclusive outcome.
"Ukraine is notorious as a place where such cases get bogged down and we may never, unfortunately, know with 100% certainty who the culprit is, although to all observers it is obvious who it is, and that is most likely the Belarusian regime," the expert told Euronews.
Crackdown on dissent
Shishov's disappearance came just a day after Belarusian athlete Krystsina Tsimanouskaya was granted a visa to travel to Poland after she said she feared for her safety if she returned to Belarus.
Tsimanouskaya claimed that, after criticising how the Olympic team was being run in Japan, Belarusian officials had tried to force her home to Belarus.
Since the August 2020 presidential vote that the West denounced as rigged, Belarusian President Alexander Lukashenko has cracked down on opposition protests in his country, prompting many dissidents to flee -- often to Ukraine, Poland and Lithuania.
Thousands of opposition demonstrators have been arrested since the disputed vote, while many NGOs and independent media have been forced into liquidation.
Belarusian exiled opposition leader Sviatlana Tsikhanouskaya tweeted on Tuesday that she was "devastated" by Shishov's death.
"It is worrying that those who flee Belarus still can't be safe," she said.
"It's not the first time a political assassination in Kyiv, it sends a message that Ukraine is not a safe territory for these exiles," Zalmayev told Euronews.
Lukashenko is "sending a message to the rest of the community to stay quiet, to not stir the boat, and not to welcome any more refugees," the expert said.