Tunisia's presidential candidate Nabil Karoui received a hero's welcome as he walked free from jail Wednesday, just days ahead of a runoff against a political newcomer.

Just weeks after Tunisians rejected ruling political parties in the first round of presidential polls, voters are set to return to the ballot box on Sunday to elect a new parliament.

Former Tunisian president Zine El Abidine Ben Ali, the first leader to be toppled by the Arab Spring revolts, died Thursday in Saudi Arabia, Tunisia's foreign ministry told AFP. He was 83.

Political outsider Kais Saied was leading Tunisia's election with just over a quarter of votes counted, the election commission said Monday, in the country's second free presidential vote since the Arab Spring. 

Tunisia will hold on Sunday its second free presidential election by universal suffrage since the 2011 uprising that toppled an autocratic regime, with growing uncertainty over who will reach the next round.

Eight years after triggering the Arab Spring, Tunisia is held up as a model of democratic transition, while other countries that experienced the mass uprisings are gripped by chaos, repression or war.

Rushing to register candidates and train poll workers, Tunisia's electoral commission has raced to organise presidential elections after the death of leader Beji Caid Essebsi, hoping to protect the country's nascent democracy.

Tunisia's Prime Minister Youssef Chahed announced Thursday he would stand in presidential elections next month.

Tunisia has less than two months to organise snap elections following the death of president Beji Caid Essebsi, amid uncertainty over who could step forward to run the North African country.

Prime Minister Youssef Chahed decided Friday to ban the niqab Muslim face covering for women in Tunisian government offices "for security reasons", his office said.