Moscow's aim was to bring more pro-Russian candidates into the European Parliament, said Prime Minister Alexander de Croo.

"Weakened support for Ukraine serves Russia on the battlefield," he said.

The Czech government said recently that it had broken up a pro-Kremlin network.

Intelligence agencies both in Prague and Poland said the Voice of Europe news website had been funded by Moscow to spread propaganda and funnel cash to sympathetic European politicians. The website has not responded to the allegations.

Referring to the Czech revelations, Prime Minister Alexander de Croo said Belgian intelligence had confirmed that spy networks were operating in Belgium and several other European countries.

"The investigation shows that Moscow has approached European members of parliament, [and] has also paid European members of parliament in order to promote a Russian agenda here," the Belgian prime minister said.

He said Belgian authorities had launched a prosecution but did not give names of anyone suspected of receiving money. No cash payment had taken place in Belgium itself although pro-Russian interference was going on, he explained.

A number of politicians on the far right in Europe are viewed as sympathetic to Russia. Czech reports have suggested that the Voice of Europe paid politicians from Germany, France, Poland, Belgium, the Netherlands and Hungary in exchange for making pro-Russian remarks to help influence the 6-9 June elections.

Earlier this week a candidate for Germany's far-right AfD party, Petr Bystron, "vehemently denied" allegations in Czech media that he had received Russian cash.

Moscow's aim was to bring more pro-Russian candidates into the European Parliament, the Belgian leader said, adding that he had been in touch with his Czech counterpart and the heads of the European Commission and European Parliament.

"We cannot allow this type of Russian menace in our midst," he said, emphasising that his country had a responsibility to ensure a free and safe vote during the European Parliament elections.

The Belgian capital Brussels is both home to the EU's executive, the European Commission, and one of the homes of the Parliament.

Czech Prime Minister Petr Fiala has warned that actions of the pro-Russian network risk having a serious impact on both Czech and EU security. His government has imposed sanctions on both the Voice of Europe website and two pro-Russian Ukrainians.