Belarus authorities rounded up more than 450 people who responded to anonymous Internet-based calls for anti-government rallies across several cities.

Thousands turned out for the Wednesday night demonstrations, marking their protests by clapping their hands while walking down city sidewalks.

Most of those detained were released on Thursday, but at least 20 were taken to court on charges of petty hooliganism.

Sweden's Foreign Ministry said Thursday one of its diplomats was harassed by security officials during the gathering, and summoned the Belarusian ambassador in connection with the incident.

Wednesday's clapping marches were the biggest anti-government turnout since protests last December were called to denounce the results of the presidential elections, which were widely seen as fraudulent.

President Alexander Lukashenko has led a harsh crackdown since December on opposition leaders, activists and journalists.

Victor Martiovich, editor of the opposition newspaper Belgazeta, said the government now is facing an amorphous civilian opposition with no clear hierarchy or leadership.

Opposition leader Anatol Lebedko called the latest rally a success.

Mr. Lukashenko, Belarus' leader for the last 17 years, has threatened to shut down the Internet.

Security services already have blocked Internet access to several political opposition sites and interrogated hundreds of Facebook users.