Oil-rich Congo's government has called an October referendum on allowing veteran leader Denis Sassou-Nguesso, who has already notched up more than 30 years in power, to run for a controversial third term.

The 72-year-old is currently barred by the constitution from seeking another presidential term as there is an age limit of 70 as well as a ceiling of two mandates.

President Sassou-Nguesso is among several African leaders who have sparked controversy by seeking to extend his stranglehold on power and the move provoked a massive protest in the country's capital Brazzaville when announced last month.

Similar recent moves by his peers have resulted in violence, notably in nearby Burundi where President Pierre Nkurunziza's controversial and globally condemned third term has sparked an abortive coup and a sweeping crackdown.

Late last year, the iron-fisted ruler of Burkina Faso, Blaise Compaore, was toppled by popular street protests after trying to prolong his 27-year-rule and a recent coup attempt by one of his closest aides only lasted a week.

The Congolese government said late Monday that the October 25 referendum would be on scrapping both the two-term limit for presidential candidates and the age cap.

"After an enriching debate...the Council of Ministers, with each member fully conscious of the historic character of the event, voted to adopt the project to reform the constitutional law," a statement said.

"The referendum is fixed for October 25," it said, adding that the campaign period would run from October 9 to 23.

The proposed amendment would also whittle down the presidential term from seven to five years.

Demonstrations

In August, President Sassou-Nguesso sacked two ministers who came out against plans to extend his mandate without giving any official reason.

In late September, thousands of people demonstrated in a rare protest in Brazzaville, the biggest since the Congolese leader returned to power in 1997, dubbing the planned changes a "constitutional coup".

Slogans such as "Sassou out!" echoed through Brazzaville's central Boulevard des Armees as some protesters carried banners reading "Sassoufit", a play on words that sound like "that is enough" in French, the nation's official language.

The roughly two-hour demonstration ended without violence, though some local businesses closed up early fearing there might be trouble.

The Congolese strongman served as president from 1979 until 1992. He then served as opposition leader and returned to power at the end of a brief civil war in 1997.

He was elected president in 2002, then again in 2009, prompting cries of fraud from his foes.

President Sassou-Nguesso had previously convened a "national dialogue", which came out "by a large majority" in favour of amending the constitution to remove the term and age limits.

"The time of change is upon us because we have already had more than 30 years with the same leader," said Mathias Dzon, a leader from opposition group Frocad during the Brazzaville protest on September 28.