Meta Platforms' Facebook and Instagram have failed to tackle deceptive advertising and disinformation ahead of key European Parliament elections, the European Commission said on Tuesday as it opened an investigation into suspected breaches of EU online content rules.

The move by EU tech regulators came amid concerns about Russia, China and Iran as potential sources of disinformation, but also inside the EU, with some political parties and organisations seeking to attract voters with lies in the June 6-9 vote to select the next five-year parliament.

The Digital Services Act which kicked in last year requires Big Tech to do more to counter illegal and harmful content on their platforms.

"We suspect that Meta's moderation is insufficient, that it lacks transparency of advertisements and content moderation procedures," EU digital chief Margrethe Vestager said in a statement.

"So today, we have opened proceedings against Meta to assess their compliance with the Digital Services Act," she said.

The Commission said it suspects that Meta does not comply with DSA obligations related to addressing the dissemination of deceptive advertisements, disinformation campaigns and coordinated inauthentic behaviour in the EU.

It also singled out the non-availability of an effective third-party realtime civic discourse and election-monitoring tool ahead of the elections to the European Parliament.

The Commission also cited concerns about Meta's deprecation of its disinformation tracking CrowdTangle without an adequate replacement.

Meta has five working days to inform the EU about remedial actions taken to address the concerns. DSA breaches can cost companies fines of as much 6% of their global annual turnover. (Reporting by Foo Yun Chee; Editing by Kirsten Donovan)