Russia's foreign ministry on Thursday said outdated legislation and a lack of regulation had revealed flaws in the US electoral system, as votes were being tallied to decide the next American president.

The knife-edge US presidential race was tilted toward Democrat Joe Biden early Thursday, but President Donald Trump claimed he was being cheated and went to court to try and stop vote counting.

Foreign ministry spokeswoman Maria Zakharova said that both candidates had an equal chance of winning and pointed out "obvious shortcomings in the American electoral system."

"This is partly due to the archaic nature of the relevant legislation and a lack of regulation in a number of fundamental points," she said during her weekly press briefing. 

Zakharova also said Russia hopes the United States will be able to elect the next president in "full compliance with the American constitution."

"And the most important thing is to avoid the occurrence of mass riots in the country," she added.

An observer mission from the Organization for Security and Co-operation in Europe, which monitors votes around the West and the former Soviet Union, found no evidence of election fraud and said Trump's "baseless allegations" eroded trust in democracy.

A two-year investigation into links between Russian meddling in the 2016 election and Trump's campaign confirmed troubling behaviour but eventually ended in anticlimax.