The German government on Monday voiced "strong doubts" over a disputed presidential vote in Belarus, also condemning the arrests of protesters in post-election demonstrations.

"We have strong doubts -- and from our point of view justified doubts -- about the... conduct of these elections," government spokesman Steffen Seibert told a press conference.

"Minimum standards for democratic elections were not met" and this was "not acceptable", he said, adding that "the numerous reports of systematic irregularities and violations of electoral law are credible."

Berlin also condemned the "use of violence against peacefully demonstrating people" as well as "numerous arrests".

"The political leadership of the country must accept the will of its citizens," Seibert said. 

Belarus on Monday declared a landslide election victory for strongman Alexander Lukashenko after police used stun grenades, tear gas and rubber bullets to disperse protesters denouncing the vote as a fraud.

The protests erupted after an exit poll for Sunday's election showed Lukashenko soundly beating main opposition challenger Svetlana Tikhanovskaya.

Police in Belarus detained 3,000 people for taking part in unauthorised gatherings during post-election demonstrations on Sunday.

Tikhanovskaya on Monday she rejected the result of the vote and demanded that the authorities transfer power to the opposition.