Clashes broke out for the second straight night after the opposition accused President Alexander Lukashenko of rigging his re-election victory.
A man has died during rallies in the Belarus capital Minsk when an explosive device went off in his hand, police said, confirming the first casualty of post-election protests.
"One of the protesters tried to throw an unidentified explosive device at members of law enforcement. It exploded in his hand," the interior ministry said on Monday night, adding that he died of his injuries.
Belarus police used rubber bullets and tear gas to break up fresh protests challenging the result of a controversial weekend presidential election, witnesses and reports said.
Several thousand protesters took to the streets of the capital Minsk for a second night of post-election rallies, with opposition supporters shouting and hundreds of cars honking their horns and waving flags.
Some shouted "Shame" and "Long live Belarus," an AFP correspondent said from the scene.
Use of force
Police in full riot gear moved against the rallies, firing tear gas and rubber bullets on peaceful protesters and injuring a female journalist, a witness told AFP.
A blast from an apparent stun grenade was also heard.
Independent Belarusian media including tut.by reported the use of force.
On Sunday night, thousands also took to the streets of Minsk and other cities to denounce the vote, sparking clashes with members of law enforcement.
Police said they detained some 3,000 people, around 1,000 of them in Minsk.
Shocking images released by pro-opposition media and posted online showed police firing stun grenades and rubber bullets into the crowds and a police van ramming into the demonstration and running down a protester.
The Belarusian Investigative Committee said on Monday it had opened 21 criminal probes into "mass unrest" and using violence against police and detained more than 80 people.
"Most of them are young people aged 20-25," investigators said in a statement.
EU, US concerned
Meanwhile, the European Union and the United States have expressed over the Belarus election and the police crackdown.
In a joint statement, EU foreign policy chief Josep Borrell and the EU commissioner responsible for relations with Europe’s close neighbours, Oliver Varhelyi, lamented that "the election night was marred with disproportionate and unacceptable state violence against peaceful protesters."
"The United States is deeply concerned about the conduct of the August 9 presidential election in Belarus, which was not free and fair," US Secretary of State Mike Pompeo said in a statement.
"We strongly condemn ongoing violence against protesters and the detention of opposition supporters, as well as the use of internet shutdowns to hind er the ability of the Belarusian people to share information about the election and the demonstrations," he added.