A Tunisian court on Wednesday sentenced presidential candidate Ayachi Zammel to 20 months in prison, Zammel's lawyer said, the latest move that has heightened opposition fears of a rigged election aimed at keeping President Kais Saied in power.

Zammel, head of the opposition Azimoun party, was arrested two weeks ago on charges of falsifying voter signatures on his candidacy paperwork, charges he called manufactured by Saied.

Political tensions in the North African country have risen ahead of the Oct. 6 election since an electoral commission named by Saied disqualified three prominent candidates this month amid protests, opens new tab by opposition and civil society groups.

The commission approved only the candidacies of the incumbent president, Zammel and Zouhair Magzhaoui, who was seen as close to Saied, defying Tunisia's administrative court, the highest judicial body in election-related disputes.

"Today's verdict is politically motivated, unfair and aims to undermine his chances in the presidential race", Abdessattar Massoudi, Zammel's lawyer, told Reuters.

Rights groups, political parties and constitutional law professors protested, saying the commission's decision to defy the court was an unprecedented step that raised doubt about the legitimacy and legality of the election.

Saied was democratically elected in 2019, but then tightened his grip on power and began ruling by decree in 2021 in a move the opposition has described as a coup.

Critics have accused Saied of using the electoral commission to secure victory by stifling competition and intimidating other candidates. Saied has denied the accusations, saying he is fighting traitors, mercenaries and the corrupt, and he will not be a dictator.

Abir Moussi, leader of the Free Constitutional Party, has been imprisoned since last year on charges of harming public security. Another prominent politician, Lotfi Mraihi, was jailed this year on charges of vote-buying in 2019 election.

The two had announced their intention to run in the October election but were jailed and prevented from submitting paperwork for their candidacies.

Another court last month sentenced four other politicians who had intended to run for president to prison and a lifetime ban from running.