State police and undercover officers grabbed demonstrators at rallies in Minsk and elsewhere, where citizens held silent demonstrations about the country's economic troubles.
Belarusian authorities must immediately and unconditionally release anyone being held merely for taking part in peaceful 'silent' protests, Amnesty International said in a statement.
While BBC has confirmed 100 arrests, Amnesty is claiming that as many as 250 people were detained, some receiving sentences or fines for hooliganism.
People in Minsk met at the capital without carrying signs, instead standing silently in solidarity against the Eastern European country's leadership.
Although President Aleksandr Lukashenko, who has served for 16 years as Belarus' first and only president, warned citizens earlier this month that he would strike hard against demonstrators, the protests have largely been peaceful. Nonetheless, plainclothes policemen were seen taking away protests from major locations.
If a citizen wants to just stand on a square or a street and is not disturbing public order then there is no crime being committed ... If it is a big group ... then you have to think about the freedom of others who are returning from work ... In that case police officers can ask people to stand or clap in another place, Belarusian Minister of Justice told a meeting of factory workers on June 28.
Earlier protests saw arrests as well, and nearly 500 were detained on June 22, Amnesty claims.
Additionally, there are reports that three Polish journalists were being detained in Belarus.
According to Polish officials, the former press representative for The Union of Poles in Belarus Igor Bancer has been sentenced to five days imprisonment for petty hooliganism, and radio reporter Agnieszka Lichnerowicz was removed from outside the courthouse during before the trial of journalist Andrzej Poczobut began.
Belarus is massively in debt, and many blame Lukashenko's overspending for the problem. In June, Russia cut electricity supplies to the county by half because Belarus had yet to pay off their loans.
The country has experienced a 36 percent devaluation of its currency (the Belarusian Ruble) and 13.1 percent inflation in recent months, and is seeking a multi-billion euro bailout from the International Monetary Fund.