Thousands of people in Serbia have set up street blockades, demanding the release of anti-government demonstrators arrested during clashes with police.

The Kremlin said on Monday that it could not rule out the possibility that anti-government protests in Serbia, a close Russian ally, could be an attempted "colour revolution", but that it was sure the Serbian leadership could restore calm.

Police detained several dozen protesters, while six police officers were reported injured in clashes, Dragan Vasiljevic, the director of police, told a press conference late on Saturday. Vucic said protesters attempted to topple the state. "They (protesters) wanted to topple Serbia, and they have failed," he wrote on his Instagram page.