Belgium's Prime Minister called on the European Parliament to launch an investigation into claims of a network that had been spreading Russian propaganda by paying EU lawmakers.

The Czech Republic said on Wednesday its spies discovered the network had been spreading Russian propaganda through the Prague-based Voice of Europe news site.

Moscow also paid money to MEPs to promote Russian propaganda, Belgian Prime Minister Alexander De Croo said on Thursday.

The revelation comes a year after the "Qatargate" bribery scandal, in which a number of EU lawmakers were accused of being paid to promote the interests of Qatar and Morocco.

The EU parliament's political groups now want the assembly to probe the latest claims.

Valerie Hayer, who heads the centrist Renew grouping, wrote to parliament president Roberta Metsola to demand "a full and transparent internal investigation."

"If sitting MEPs or candidates in the upcoming European elections have taken money from the Russian government or their proxies, they must be exposed and action taken," she said.

The Renew group also called for an "urgent debate" in the parliament.

The Greens said there needed to be a "swift and thorough" investigation.

"This is how (Russian President Vladimir) Putin is trying to get away with his war in Ukraine.... It's a direct attack on the very fabric of our democracy," said Terry Reintke, one of the lead candidates for the Greens in the European elections in June.

"The politicians who have received money from Russia should be severely punished, both politically and legally," she added in a statement.

A spokesperson for the parliament said it was "currently looking into the findings of the Czech authorities regarding outlet 'Voice of Europe' in coordination with its institutional partners."

The spokesperson added that the parliament already prohibits access to the institutions for media that are on EU sanctions lists.

EU lawmakers face strict rules regarding independence and ethics and can face penalties – financial and otherwise – if they violate them.

The European politicians involved have not been named but the Greens and a Czech daily claimed they came from Belgium, France, Germany, Hungary, the Netherlands and Poland.