Vitaly Shishov, who led a Kyiv-based organisation which helps Belarusians fleeing persecution, had been reported missing by his partner on Monday after failing to return home from a run. Police said they had launched a criminal case for suspected murder, including investigating whether killers tried to disguise the crime as suicide.

       Mr Shishov had felt under constant surveillance since he left Belarus last year after taking part in anti-government protests, his colleagues said in a statement.

       He had been warned about possible threats, including being kidnapped or killed.

       A police statement said: “Belarusian citizen Vitaly Shishov, who disappeared yesterday in Kyiv, was found hanged today in one of Kyiv's parks, not far from his place of residence.”

       Ukraine, Poland and Lithuania have become havens for Belarusians during a crackdown by President Alexander Lukashenko following a disputed election last year.

       Mr Shishov led the Belarusian House in Ukraine (BDU) group, which helps Belarusians find accommodation, jobs and legal advice, according to its website.

       BDU said in a statement: "We were also repeatedly warned by both local sources and our people in the Republic of Belarus about all kinds of provocations, including kidnapping and liquidation.”

       "Vitaly treated these warnings stoically and with humour."

       The organisation had said on Monday it was not able to contact Shishov.

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       It said Shishov had left his residence at 9am local time (6am GMT) and was supposed to have returned an hour later.

       The Belarusian authorities have characterised anti-government protesters as criminals or violent revolutionaries backed by the West, and described the actions of their own law enforcement agencies as appropriate and necessary.

       BDU was set to organise a march in Kyiv on August 8 to mark a year since the start of mass protests against Lukashenko.

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       Mr Shishov's death comes at a time when eyes around the world are trained on Belarus after Olympic sprinter Krystsina Tsimanouskaya refused to board a plane to take her back to her home country from Beijing.

       Ms Tsimanouskaya's future is uncertain, although speaking yesterday Aleksandr Opeykin, chairman of the Belarusian Sports Solidarity Foundation, claimed she had been offered asylum in Poland.

       He said: "She will fly from Tokyo, a direct flight to Warsaw on August 4, in two days' time.

       “She has accepted the offer issued by the Polish Foreign Ministry to request international help, she has done that and she has received a Polish visa today.

       “We, at the Foundation, helped her to get the ticket to Warsaw.”

       Also speaking yesterday, Tory MP Tobias Ellwood, chairman of Parliament's defence committee, told Express.co.uk he feared for Ms Tsimanouskaya's safety if she was forced to go back to Belarus.

       Referring to the plight of dissident journalist Roman Protasevich, who was arrested after the flight on which he was travelling was forced to land in Belarus, the Bournemouth East MP said:“We mustn't forget about what happened on that Ryan flight with a journalist and a critical voice, where a European airline was effectively hijacked, in order to secure the arrests of a individual who've been critical of Belarus.

       “The offer of Poland providing asylum from Poland is actually welcome news but we are far from out of the water.”