ROME (Reuters) - Matteo Salvini, the leader of Italy’s right-wing League party, has been placed under criminal investigation by Rome prosecutors over suspicions he improperly used state flights, a judicial source close to the investigation said.

FILE PHOTO: League party leader Matteo Salvini speaks during an anti-government demonstration in Rome, Italy, October 19, 2019. REUTERS/Remo Casilli/File Photo

The probe into possible abuse of office concerns 35 plane and helicopter flights Salvini took when he was interior minister in the previous government which he brought down in August, when the League moved into opposition.

Ministers can use state flights for institutional reasons but not for campaigning, which is what prosecutors suspect Salvini did as he criss-crossed Italy for months, sometimes combining interior ministry functions with party rallies.

“I read that I am under investigation,” Salvini said on Thursday, after several newspapers carried reports of the investigation. “All my state flights were for state reasons ... I never took state flights to go on holiday, that’s what other politicians do.”

Italy’s audit court, which specializes in issues related to public funds, looked into Salvini’s case earlier this year.

It said his use of the flights was illegitimate but still dropped the case on the grounds that they had not caused an extra cost for the taxpayer.

The investigation is unlikely to affect support for the League, which is easily Italy’s most popular party with the backing of about 30% of voters, according to opinion polls.

Legal problems have dogged Salvini and the League for months. In February, while Salvini was still a minister, parliament blocked an investigation into accusations of kidnapping over his decision to hold 150 migrants on board a ship for five days in August 2018.

Police searched offices of the Lombardy regional government and firms linked to the League on Tuesday in a money laundering probe connected with a 2018 ruling that ordered the League to repay 49 million euros ($54 million) it owed the state.

Prosecutors also opened an investigation into possible international corruption following media reports that the League tried to raise millions of euros via a secret Russian oil deal.