Chancellor Angela Merkel's spokesman said on Monday that Germany was looking with "heightened vigilance" to the threat of Russian online meddling in the lead-up to European Parliament elections this month.

"Heightened vigilance to this issue has not only been necessary but has been practised for some time, in Germany as well as at the European level," Merkel's spokesman Steffen Seibert told a news conference in Berlin.

"Our increased attention is not without reason. We are observing carefully the online activities of different international sources - among them are Russian ones."

Seibert was responding to renewed warnings Moscow would run disinformation and manipulation campaigns ahead of the May 23-26 election, including from European Justice Commissioner Vera Jourova who called it "a central issue" in comments to German media.

The New York Times meanwhile reported that "a constellation of websites and social media accounts linked to Russia or far-right groups is spreading disinformation, encouraging discord and amplifying distrust" in mainstream parties.

In Germany, the report said, the far-right Alternative for Germany (AfD) party had received strong support from both Russian government media and unofficial pro-Russian channels.

The daily cited a former FBI analyst as saying Moscow also appeared to amplify messages from left-wing anti-fascist or Antifa groups, including calls on Twitter to join anti-AfD protests, with the apparent goal of sowing political discord.

Lithuania's Foreign Minister Linas Linkevicius gave a similar warning during an interview with German media group RND.

"The European elections are a test run of whether the defensive mechanisms against Russian influence work," he was quoted as saying. "We must not be naive: Moscow is trying to create a permanent state of instability in the EU and exploit it for its own interests."

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