Updated 8.28am

A missing Belarusian activist has been found hanged in a park in the Ukrainian capital Kiev, police said on Tuesday, adding they had opened a murder probe.

"Belarusian citizen Vitaly Shishov, who had gone missing in Kiev yesterday, was today found hanged in one of the Kiev parks, not far from where he lived," police said in a statement. 

Vitali Shishov, head of the Belarusian House in Ukraine, went jogging in Kiev on Monday morning but did not return and could not be reached on his mobile phone, his organisation said earlier before the grim discovery.

Friends of Shishov said he had been followed by "strangers" while jogging recently, human rights organisation Vyasna said on Telegram.

Police and volunteers had mounted a search of the area where he went running.

Many Belarusians have fled, often to neighbouring Ukraine, Poland and Lithuania, as President Alexander Lukashenko's regime has cracked down on any form of dissent since mass protests erupted after disputed elections last year.

Lukashenko has ruled the former Soviet republic with an iron fist since 1994.

Shishov's disappearance came as Belarusian athlete Krystsina Tsimanouskaya said she was forced to withdraw from the Tokyo Olympics and threatened with forced repatriation for criticising her athletics federation on social media. 

The sprinter, who was granted a humanitarian visa by Poland on Monday, said she feared being jailed if she returned to her country, where the authorities have targeted the president's opponents, rights activists and journalists.

Her husband Arseny Zdanevich told AFP he had fled from Belarus to Ukraine and was hoping to join his wife "in the near future".

Lukashenko and his son Viktor have been banned from Olympic events over the targeting of athletes for their political views.

Lukashenko sparked international outrage in May by dispatching a fighter jet to intercept a Ryanair plane flying from Greece to Lithuania in order to arrest a dissident onboard.