"According to the accounts of local residents who saw the attack, there were about 10 assailants armed with AK-47 rifles, and they had one heavy weapon with them," said police superintendent Kouame Lazou.

"We don't yet know the motive of this attack, but this is a very serious act," he said, adding that the attackers had fled with the weapons of the murdered soldiers.

The West African nation, the world's biggest cocoa producer, is recovering from a decade of political deadlock and civil unrest.

Last year's conflict erupted after then President Laurent Gbagbo refused to acknowledge his defeat to rival Alassane Ouattara in an election in late 2010.

Yopougon was one of the final pro-Gbagbo strongholds to fall to Ouattara's French and United Nations-backed forces as they seized the city. Gbagbo, who was captured during the fighting, is currently awaiting trial before the International Criminal Court in The Hague on war crimes charges.

While Ouattara, now president, has managed to improve security in most of the country, Ivory Coast is still awash with weapons left over from the conflict and sporadic violence continues, particularly in the volatile western cocoa heartland.

The army has taken over many policing functions since last year's conflict, as many policemen fought on behalf of Gbagbo.

Seven United Nations peacekeepers were killed on June 8 in an ambush near the town of Tai, close to the border with Liberia, in what Ivorian authorities said was a cross-border raid by pro-Gbagbo militia and Liberian mercenaries.