The Belarus Interior Ministry said the protester had died in clashes with police in the capital, Minsk, on Monday evening as thousands protested for a successive night after official results from Sunday's poll gave an overwhelming victory to authoritarian President Alexander Lukashenko, extending his 26-year rule until 2025.
Ministry spokesman Alexander Lastovsky said the victim intended to throw an explosive device, but it blew up in his hand and killed him.
The development came after scattered groups of opposition supporters began gathering in central Minsk on Monday evening, chanting “Freedom!” and “Long live Belarus!", while heavy police contingents were deployed to block central squares and roads.
Later, about 1,000 demonstrators gathered near a big shopping mall in central Minsk, and police used stun grenades and rubber bullets to disperse them.
The Viasna rights group said demonstrators had also gathered in several other cities across the country - which is home to some 9.5 million people - including Brest, Mogilev and Vitebsk, where detentions also took place.
The unrest came after Mr Lukashenko, 65, repeated allegations that shadowy forces abroad were trying to manipulate protesters he called “sheep” in order to topple him, something he said he would never allow.
“They are trying to orchestrate mayhem,” he said. “But I have already warned: there will be no revolution.”
Election officials said Mr Lukashenko won a sixth term in office with 80 per cent of the vote during the weekend's election, while opposition challenger Sviatlana Tsikhanouskaya got 10 per cent.
Ms Tsikhanouskaya, the wife of a jailed opposition blogger, dismissed the official results as a sham and submitted a formal request for a recount to the Central Election Commission.
“We don’t agree with (election results), we have absolutely opposite information,” Ms Tsikhanouskaya told the Associated Press. “We have official protocols from many poll stations, where the number of votes in my favour are many more times than for another candidate.”
The 37-year-old had managed to unite opposition groups in the run-up to the vote and drew tens of thousands to her pre-election campaign rallies, assembling some of the biggest crowds since the fall of the Soviet Union in 1991 as she tapped into fatigue with Mr Lukashenko’s autocratic rule.
After submitting her recount request on Monday, Ms Tsikhanouskaya said: “I have made a decision, I must be with my children.”
She had earlier sent her children to an unspecified European country after receiving threats.
Ms Tsikhanouskaya later fled Belarus and is now “safe” in Lithuania, according to the country’s foreign minister, Linas Linkevicius.
— Linas Linkevicius (@LinkeviciusL)August 11, 2020
Belarus' wider political opposition meanwhile also accused Mr Lukashenko of rigging his re-election victory, with dozens injured and thousands detained during protests which took place just hours after the vote.
Sunday's demonstrations saw police break up mostly young protesters with tear gas, water cannons and stun grenades and beat them with truncheons. Rights activists said one person died after being run over by a police truck, which the authorities denied.
Mr Lukashenko’s economic management and swaggering response to the coronavirus pandemic, which he has airily dismissed as “psychosis”, has fuelled broad anger and swelled the opposition ranks, with the post-election protests marking a previously unseen level of violence.
The Interior Ministry said 89 people were injured during the demonstrations late Sunday and early Monday, including 39 law enforcement officers, and about 3,000 people were detained, 1,000 of them in Minsk. It insisted that no one was killed during the protests and called reports about a fatality “an absolute fake”.
Meanwhile, Mr Lukashenko's handling of the unrest was met with a chorus of criticism from Western leaders.
The police crackdown drew rebukes from European capitals and is likely to complicate Mr Lukashenko’s efforts to mend ties with the West amid tensions with his main ally and sponsor, Russia.
The European Union condemned the police crackdown and called for an immediate release of all those detained.
In a joint statement, EU foreign policy chief Josep Borrell and the EU commissioner responsible for relations with Europe’s close neighbours, Oliver Varhelyi, said “the election night was marred with disproportionate and unacceptable state violence against peaceful protesters”.
“The Belarusian authorities must ensure that the fundamental right of peaceful assembly is respected,” they said.
Belarus’s EU and Nato neighbours Poland and Lithuania also issued strong rebukes. Polish prime minister Mateusz Morawiecki called on EU leaders to convene an extraordinary summit to support the Belarusian people’s democratic aspirations.
The UK Foreign Office also urged Belarusian authorities to “refrain from further acts of violence following the seriously flawed presidential elections” and warned that ”the attempts by Belarusian authorities to suppress protests are completely unacceptable”.
US Secretary of State Mike Pompeo meanwhile said Sunday's presidential vote was “not free and fair” and condemned “ongoing violence against protesters and the detention of opposition supporters.”