Loyalists of ousted Tunisian leader Zine al-Abidine Ben Ali will mount a coup if Islamists take power in democratic elections, the country's former interior minister warned on Thursday.

Tunisia's main Islamist group Ennahda, led by moderate Muslim scholar Rachid Ghannouchi and banned under Ben Ali, says it will contest an election slated for July after 23 years of one-man rule.

Experts say the movement could poll well, particularly in the conservative south where there is deep frustration over poverty and unemployment.

Ben Ali's ouster in January in the first of the uprisings to rock the Arab world has awoken religious tensions in the sleepy Mediterranean state between pro- and anti-Islamists.

"If Ennahda takes power, there will be a coup d'etat," Farhat Rajhi, who took over as Tunisian interior minister soon after the revolution, said in a video shared on Facebook.

"The people of the coast are not disposed to give up power and if the elections go against them, there will be a coup d'etat," he said.

The 'people of the coast' is a reference to Ben Ali loyalists who have their power base in and around the coastal city of Sousse, the former president's hometown. Ben Ali himself fled with his wife in January to Saudi Arabia.

Rajhi is considered relatively independent, and a shrewd observer of Tunisian politics. But Ennahda officials said they did not believe a coup was likely.

"We do not yet have an official position on the declaration by Mr. Rajhi but I can tell you that we have faith in all the elements of the state and in the people to respect the will of the people," Ennahda executive bureau member Nourdine Bhiri told Reuters.

A second senior Ennahda official, Ajmi Ourimi, told Tunisian radio: "General Rachid Ammar (military chief of the general staff) promised before the Tunisian people that he will protect the revolution and we have faith that everything will proceed in a peaceful environment."

The July 23 vote will be for an assembly which will draft a new constitution.

Rajhi was made interior minister soon after the revolution and replaced in March in the latest shakeup of a caretaker government struggling to keep Tunisia's shaky transition to democracy on track.

Neighbouring Algeria plunged into chaos in 1992 when the military-backed government scrapped a legislative election that a radical Islamist party was poised to win.

According to independent estimates, 200,000 people were killed in the violence that ensued.