Belarus police will now be permitted to use combat weapons in the streets if needed to respond to what the Interior Ministry described as increasingly radicalised mass anti-government protests.

Police said they had detained 713 people at mass protests on Sunday in which security forces used water cannon and batons to break up crowds demanding a new presidential election.

Tens of thousands of Belarusians have demonstrated every weekend since an Aug 9 election in which President Alexander Lukashenko was declared the winner.

His opponents say the result was falsified; Lukashenko denies rigging the vote. Most opposition leaders have fled the country or been arrested.

"The protests, which have shifted largely to Minsk, have become organised and extremely radical," the Interior Ministry said in a statement.

"In this regard, the Interior Ministry's employees and internal troops will not leave the streets and, if necessary, will use special equipment and military weapons," it said.

Western countries have imposed sanctions against Belarusian officials they blame for election fraud and the abuse of protesters. Germany's Foreign Minister Heiko Maas said on Monday Lukashenko should be added to an EU sanctions list which includes around 40 other Belarusian officials.