Thousands of people have held a mass demonstration in the Republic of Congo to protest against plans by President Denis Sassou Nguesso to extend his rule.

A huge demonstration was staged in the capital, Brazzaville, on Sunday against the veteran ruler's plan for a constitutional referendum that would let him extend his rule.

During the rally which lasted two hours, the protesters chanted slogans like "No to a third term, No to a constitutional coup" and "No to a referendum."

The rally, stretching for almost a kilometer along a main boulevard in the city center, was the biggest since Sassou Nguesso returned to power in 1997.

If the referendum is approved Sassou Ngeusso would be eligible to contest in the elections next year.

The changes effectively pave the way for him to stand for a third term in 2016. The opposition has dubbed the forum's conclusions a "constitutional coup."

Sassou Ngeusso, 72, was president from 1979 until 1992. He then served as opposition leader and returned to power following a brief civil war in 1997 after his rebel forces deposed then president Pascal Lissouba.