Belarussian courts have jailed more than 150 opposition protesters following demonstrations against the president's landslide election victory.
Arrested protesters complained of ill-treatment by police
Those sentenced to up to 15 days in jail included Mariusz Maszkiewicz, a former Polish ambassador to Belarus.
President Alexander Lukashenko's re-election on 19 March has been widely condemned as fraudulent by the opposition and by Western observers.
A runner-up in the election, Alexander Kozulin, is also in jail.
He could face up to six years in jail on hooliganism charges, correspondents report.
Mr Kozulin was arrested when police broke up an opposition rally in Minsk on Saturday. He is being held in a jail in Zhodino, 40km (25 miles) north-east of the capital.
Mr Kozulin complained of back and knee pain after being beaten by police, his lawyer Igor Rynkevich told the Associated Press news agency.
Poland has complained that Mr Maszkiewicz was beaten up after he was detained.
Another Polish diplomat, the consul in the western city of Grodno, has been prevented by Belarussian customs officers from entering the country.
Belarussian state television accused consul Ianusz Dabrowski of smuggling in publications denigrating Belarus and of meeting "radical" opposition activists.
The EU has voiced outrage at the arrest of Mr Kozulin and other protesters, demanding their immediate release.
Belarussian Interior Minister Vladimir Naumov said Mr Kozulin had been arrested because he had called for people to rise up against the state.
Belarus insists Mr Lukashenko's win was fair.
The US and EU have agreed to impose sanctions on Belarus, likely to include a travel ban against Mr Lukashenko.
Canada has decided to limit its official relations with Belarus and has demanded the release of Frederick Lavoie, a Quebec journalist arrested while covering the demonstrations in Minsk.