Belarus authorities deployed water cannons on Wednesday to disperse protesters who had gathered in central Minsk to denounce the secret inauguration of President Alexander Lukashenko.
Several dozens of protesters were also arrested, AFP reported.
Lukashenko was sworn in for his sixth term on Wednesday in front of several hundred top government officials but the ceremony was kept secret.
Protests against his election victory have been ongoing since the August 9 presidential election in which he was credited with over 80% of the vote. The opposition, the European Union and the United States have rejected the official results.
The 66-year-old president has ruled over the ex-Soviet country for 26 years.