The Comoros at a glance
One of the world's poorest countries, the Indian Ocean island nation of the Comoros has endured years of political turmoil, including a spate of coups.
Here is a factfile of its controversial referendum, which could allow President Azali Assoumani to extend his term:
'Islands of the Moon'
Made up of the three islands of Anjouan, Grande-Comore and Moheli, the small country's land surface is 1 870 square kilometres, with a population of just 800 000.
The Comoros, which means "Islands of the Moon" in Arabic, are situated between Madagascar and Mozambique, and next to the French-administered island of Mayotte.
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The Comoros Islands embraced Islam in the 12th century and its people are now 99% Muslim, mostly Sunnis.
Besides provisions on the presidential term, the proposed constitution would wipe out the notion of secularism to make Islam the state religion, based on "the principles and rules of Sunni observance".
Mayotte: tensions with France
The Comoros became independent from France in 1975, breaking away in a referendum in which Mayotte was the only island in the archipelago that opted to remain with the colonial-era power.
However the country still claims Mayotte, in which it is backed by several UN resolutions, in a territorial dispute with France.
Mayotte is relatively well-off compared to the impoverished and unstable Comoros, and grapples with a flood of illegal migrants who often make the 70km crossing in makeshift boats.
Since independence, the Comoros has endured more than 20 attempted coups, four of which were successful.
The first president, Ahmed Abdallah, was ousted a month after independence with the help of renowned French mercenary Bob Denard.
Three years later Denard organised a coup to reinstate Abdallah and became army chief.
In 1989 Abdallah was assassinated in as yet unexplained circumstances. Denard, then head of the presidential guard, tried to take control but fled as France intervened militarily.
Anjouan seceded in 1997 only rejoining the other islands in 2001, the year a new constitution created the Union of the Comoros that gave the islands more autonomy, rotating the presidency between them.
Assoumani, whose decision to organise a referendum to change the constitution has led to deep tensions, seized power in a coup in 1999.
He was re-elected in a 2016 vote marred by violence and allegations of irregularities.
Ylang-ylang and poverty
Lacking the major tourist infrastructure of the Indian Ocean islands of Mauritius and the Seychelles, the country's main activities are fishing and agriculture.
Vanilla, cloves and above all ylang-ylang - the tree whose fragrant oil is used to make perfume - are the principal sources of hard currency.
But the country is poor and heavily dependent on remittances from emigrants, notably in France which is home to 200 000-300 000 Comorans.
The Comoros trails at the bottom of the UN's Human Development Index - which compares life expectancy, education and standards of living around the world - placed at 160 of 188 countries in 2016.
The World Bank says the archipelago has to combat famine and malnutrition.
Economic growth has accelerated moderately, reaching 2.5% in 2017, largely due to better electricity supplies and increased remittances from the diaspora, the bank says.