European Union voters are set to be bombarded with lies and disinformation from outside and within the bloc in the June election for the new European Parliament, the president of the assembly warned on Tuesday.

"It is something that we have warned about for a long time. In fact, it is not just a threat," Roberta Metsola told Reuters in an interview.

She spoke just as information emerged that German authorities arrested an aid to an EU lawmaker on suspicion of espionage for China.

Metsola said she expected disinformation to feature "very heavily" in the June 6-9 vote to select the next five-year parliament.

The EU lawmaker from Malta said the bloc had tools such as a new EU law requiring social media platforms to remove illegal content and mitigate against risks of electoral manipulation, which could include fake images or voter impersonation.

However, new EU laws alone were not enough.

Metsola listed Russia, China and Iran as potential sources of disinformation, but also inside the EU, with political parties and organisation seeking to attract voters with lies.

"We've maybe ignored that for far too long," she said.

"I think we have to very much counter that narrative. It is much easier to run a black and white campaign than a 1,000 shades of grey in the middle campaign. But we have to be ready to do it," she continued.

(Reporting by Philip Blenkinsop; Editing by Ros Russell)