The head of a group that helps Belarusian citizens flee their homeland has been found dead in Ukraine.
Vitaly Shishov, 26, was discovered hanged in a park near his home in Kiev on Tuesday.
Police in the Ukrainian capital vowed to pursue all leads, including “murder disguised as a suicide”.
Shishov went jogging on Monday morning but did not return and could not be reached on his mobile phone.
Friends of the activist say he had recently been followed by “strangers” while jogging, the human rights organisation Viasna said.
Many people have fled Belarus, often to neighbouring Ukraine, Poland and Lithuania, since its president cracked down on dissent.
Mass protests broke out after Alexander Lukashenko – who has been in office since 1994 – was re-elected in a poll denounced as rigged by western governments.
Shishov moved to pro-western Ukraine in autumn last year after joining anti-government protests in Belarus.
The charity he ran in Kiev, the Belarusian House, accused the Lukashenko regime of being behind his death.
“There is no doubt that this is an operation planned by Chekists to liquidate a Belarusian who presented a true danger to the regime,” it said, referring to security service agents.
The organisation said Shishov had been involved in everything from helping fellow compatriots to settle in Ukraine to staging anti-regime protests.
It also said it had repeatedly received warnings about possible “provocations, including kidnapping and liquidation”.
Belarusian authorities have used force to put down demonstrations against Mr Lukashenko’s rule and are trying to snuff out remaining dissent by jailing university students and shutting down independent media.
UK Prime Minister Boris Johnson is due to meet Belarusian opposition leader Sviatlana Tsikhanouskaya on Tuesday.
Ahead of the talks, she said: “I want the British Government to keep Belarus on the agenda, taking into consideration all the violence that’s going on inside the country and… the threat that the regime now is for the international community.”
On Sunday, Belarusian athlete Krystsina Tsimanouskaya told police in Japan she had been forced to withdraw from the Tokyo Olympics and threatened with forced repatriation for criticising her country’s athletics federation.
The sprinter, who is sheltering in Poland’s Japanese embassy after being granted a humanitarian visa, said she feared being jailed if she returned home.
On Tuesday, US Secretary of State Antony Blinken accused Belarus of an “act of transnational repression”. Warsaw has denounced what it calls a “criminal attempt” to kidnap the athlete.
“We have made sure that Krystsina Tsimanouskaya is safe in the Polish embassy in Tokyo and we will, if necessary, offer her the possibility of continuing her career,” Polish Prime Minister Mateusz Morawiecki said.
The athlete was expected to stay at the embassy in Tokyo until leaving for Warsaw, possibly as soon as Wednesday, Poland-based dissident Pavel Latushka wrote on Twitter.
Tsimanouskaya, a 200 metres specialist, criticised the Belarusian athletics federation after it tried to force her to run in a relay at short notice. She said that outburst had led to the attempt to forcibly send her home.
Her husband, Arseny Zdanevich, told AFP on Monday he had fled from Belarus to Ukraine and hoped to join his wife “in the near future”.