(AFP) - The Comoros opposition on Saturday demanded the "re-establishment of democratic institutions" in protest at a planned July referendum on constitutional reform, which could allow President Azali Assoumani to seek re-election.

Assoumani only took office in 2016 but wants to hold a fresh vote next year, two years early, so that he can remain in power beyond 2021 when his currently non-renewable term would otherwise end.

The referendum, scheduled for July 29, could change the current system -- which sees power rotate every five years between the archipelago’s three main islands -- and allow Azali to run for two fresh five year-terms.

Friday saw demonstrations in several towns in the volcanic Indian Ocean archipelago off Africa’s east coast against the proposed poll, one of a number of controversial Azali initiatives.

He has suspended the constitutional court and also placed under house arrest opposition leader and predecessor Ahmed Abdallah Sambi, a leading critic who has urged protests against the vote.

Friday saw a third a straight week of protests and clashes between police and opposition supporters shouting "Azali out" after prayers at the Al-Qasimi mosque in the capital Moroni.

The secretary general of Sambi's party, Ahmed el-Barwane, was one of two people arrested there while another protest took place at Mbeni, the home town of Mohamed Ali Soilih, who Azali defeated for the presidency two years ago.

At Mutsamudu, capital of the island of Anjouan, one of three islands constituting the archipelago of some 800,000 people, police dispersed groups of youths demanding Sambi's release.

Opposition spokesman Mohamed Abdou Soimadou said the people want the "re-establishment of democratic institutions, notably the constitutional court, before any idea of a referendum".

He said there had been some 20 nationwide protests against the idea and "the people themselves have taken up the fight to demand a state based on the rule of law."

The Comoros, which became independent from France in 1975, has endured several political crises over the years including a spate of coups.

A new constitution was adopted in 2001 which stipulated the rotation of power every five years between the islands -- Anjouan, Grande-Comore, from where Azali hails) and Moheli.

Azali was previously in power after a bloodless 1999 coup. He stayed in office until 2006 after winning a first multi-party election and then handed power over after losing the poll that year to Sambi.

© Agence France-Presse