A Supreme Court justice ruled Wednesday President Jair Bolsonaro should be investigated for unproven claims Brazil's voting system is riddled with fraud, adding the far-right leader to an ongoing probe on the spread of fake news by his government.

The ruling by Justice Alexandre de Moraes came after Bolsonaro stepped up his longtime attacks on Brazil's electronic voting system, claiming -- without evidence -- that it is fraud-plagued and insisting there will be no elections next year as scheduled if it is not overhauled.

The Superior Electoral Court had asked the Supreme Court to issue the ruling, after itself putting the president under investigation for his campaign against Brazil's voting system.

The Supreme Court agreed, finding Bolsonaro should face investigation for slander and inciting criminal acts for his undocumented claims of massive vote fraud.

The electoral court's own probe will investigate the president for abuse of office, improper use of official communication channels, corruption, fraud and other potential crimes.

Bolsonaro has long criticized electronic voting, introduced in Brazil in 1996.

He has stepped up his attacks in the build-up to the October 2022 elections, insisting on "printable and auditable" paper ballots as a backstop to the electronic system.

Opinion polls place the 66-year-old leader well behind leftist ex-president Luiz Inacio Lula da Silva in the presidential race.

There are fears Bolsonaro could try to use fraud claims to undermine the election if he loses, following in the footsteps of former US president Donald Trump, with whom he is often compared