Rafizi Ramli is the second opposition leader to be investigated under a law passed in April that criminalizes "fake news".

On Wednesday, police said they were investigating Mahathir Mohamad, the opposition's prime minister candidate, over claims his plane was sabotaged in the run-up to next week's election.

The May 9 election pits Prime Minister Najib Razak against 92-year-old former premier Mahathir.

Read: Mahathir Challenges Malaysian Govt of Plane Sabotage Claim

Rafizi is under investigation over his remarks on social media about the filing of nomination papers for the election at a district in Negeri Sembilan state, Bernama reported, citing the state's police chief Noor Azam Jamaludin.

Rafizi said an opposition candidate was not allowed to file his nomination papers.

He did not immediately respond to comment as quoted by Reuters.

Najib's government passed a law in April that criminalizes "fake news", making it one of the first countries to do so. Critics have said the law is aimed at curbing dissent and free speech ahead of the election.

On Monday, a Danish citizen was convicted for inaccurate criticism of police on social media, the first person to be prosecuted under the new law.

Read: Malaysia's Election Campaign Kicks Off

Rafizi, a senior leader with the People's Justice Party (PKR), was sentenced to jail in February for revealing confidential bank details in a 2012 graft scandal.

REUTERS