Protesters moved in to the main streets after special forces closed off October Square, the site of a tented protest camp cleared away by police on Friday.

During the protest, police detained one of the two opposition leaders who lost to President Alexander Lukashenko in elections a week ago, witnesses said.

Opposition supporters said riot police had pulled Alexander Kozulin out of a crowd of protesters marching on a detention centre where about 200 of their comrades are being held.

Separately, Interfax news agency reported that Alexander Milinkevich, the main leader of the opposition, had also been detained but an aide denied the report.

Earlier on Saturday, Milinkevich told thousands of supporters that he had formed a "Popular Movement for the Liberation of Belarus."