Sporadic violence flared in Ivory Coast on Saturday after President Alassane Ouattara was chosen by his ruling party to run for a third term in an October election, despite furious opposition charges the move is unconstitutional.

Ouattara, in power since 2010, said in March he would not stand again but changed his mind after the death of prime minister Amadou Gon Coulibaly -- seen as his anointed successor -- of a heart attack in July.

 After his official nomination on Saturday, Ouattara vowed to score a first-round knockout victory before tens of thousands of supporters at an Abidjan rally.

 "Going back on my decision was not easy," said Ouattara, who insisted: "There is nothing preventing me from standing."

 "I did not have the right to place my personal project above the urgent situation in which the country finds itself," he said.

 But his party's decision provoked outrage among young opposition supporters who took to the streets to voice loud and violent protest in several major cities. 

 The constitution limits presidents to two terms, but 78-year-old Ouattara and his supporters argue that a 2016 constitutional tweak reset the clock, allowing him to seek a third.

 Opposition and civil society groups say his standing again amounts to a "coup" that risks triggering chaos in the world's biggest cocoa producer.

 Violence erupted in several towns, notably Divo, a cocoa-growing centre 200 kilometres (125 miles) northwest of Abidjan where pro-opposition youths clashed with young supporters of the ruling party.

 "There are people wounded. The small bus station, bars and shops have been set on fire and looted," Davo's political representative Famoussa Coulibay told AFP.

 "There have been police reinforcements. We will try to calm things down with the leaders of the community," Coulibay added.

 Gagnoa, the home town of former president Laurent Gbagbo further to the northwest, also saw unrest.