Belgium on Friday announced it is probing Russian "interference" in the European Parliament following allegations that lawmakers took money to spread Kremlin propaganda ahead of the June EU elections.

The Czech Republic last month said its intelligence service had discovered a network that used EU lawmakers to spread Russian propaganda through the Prague-based Voice of Europe news site.

Belgium says it has determined that some of the lawmakers had been paid to promote Moscow's propaganda.

"The cash payments did not take place in Belgium, but the interference does. As Belgium is the seat of the EU institutions, we have a responsibility to uphold every citizen's right to a free and safe vote," Belgian Prime Minister Alexander De Croo said.

A summit of EU leaders next week will discuss the allegations, raised two months ahead of the June 6-9 bloc-wide elections to vote in a new European Parliament.

De Croo said Moscow's "clear" objectives were to "help elect more pro-Russian candidates to the legislature and reinforce the pro-Russian narrative in that institution."

Belgium's federal prosecutor's office confirmed that the probe into foreign individuals or organisations suspected of giving "donations, loans or advantages" to gain influence started on Thursday.

The crime carries penalties ranging from six months to five years in prison and a fine of between 1,000 and 20,000 euros (US$1,050-US$21,250).

"If there would be a type of bribery – and our services indicate that payments have taken place – while you need two sides for that to happen, you have people who organise it, but you also have people to receive it," De Croo said.

The European Commission has issued repeated warnings about Moscow spreading disinformation and misinformation ahead of the EU polls, and seeking to weaken European public support for Ukraine as it fights off Russia's assault.

Tactics go beyond publishing outright false information, EU officials have said. Mixing in nuggets of facts into false stories can confuse or mislead readers so that they distrust all news sources – including reputable ones.

Voice of Europe, whose internet site is still accessible, is known for publishing stories repeating Russian messaging and giving airtime to guests who do so.

One of its top executives is a Ukrainian oligarch, Viktor Medvedchuk, who is close to Russian President Vladimir Putin and who has been sanctioned by the Czech government along with the outlet itself. (AFP)