Paul Koffi Koffi said the raid on Friday afternoon highlighted the need for Ivorian troops to carry out cross-border operations in Liberia to improve security. Liberia's government said it would issue a statement later in the day but the United Nations said it was reshuffling some of its several thousand troops deployed in the zone to protect civilians in the border area.
The attack highlights simmering tensions and security threats in the west of the world's top cocoa grower despite a year of progress that stabilised much of the rest of the country after months of post-election violence last year.
"These people came from the other side of the border. They are militias and mercenaries," Koffi Koffi said. "We must go to the other side of the border to establish a security zone. We will clean up and secure the zone. This will be done, of course, with the agreement of the two countries."
Ivory Coast and Liberia have good relations and have in the past carried out joint patrols with UN peacekeepers along their border. Koffi Koffi said "one or two" Ivorian soldiers were killed alongside the peacekeepers, who were responding to a suspected raid on a village 45 km south of the town of Tai, close to the border, when they were ambushed.
The United Nations' humanitarian coordination office, OCHA, said an old woman was among the eight civilians killed. It said hundreds of civilians from the raided village had arrived in Tai after fleeing the violence.
"We're expecting around 4,000 that are reportedly on their way there," Anouk Desgroseilliers, OCHA spokeswoman in Ivory Coast, told Reuters.
Alassane Ouattara won a 2010 election but only came to power following months of violence that killed thousands after incumbent Laurent Gbagbo refused to concede. New York-based Human Rights Watch warned earlier this week that Liberian mercenaries and Ivorian fighters who fought on behalf of Gbagbo in the brief civil war last year were launching attacks on Ivory Coast from Liberia.
The campaigning group said the militants behind the raids, which have killed 40 people since last July, were receiving funds from supporters of Gbagbo - who is awaiting trial for crimes against humanity at the International Criminal Court in The Hague over his role in the civil war. Liberia has denied accusations it is not doing enough to prevent the attacks.
After the raid on Friday, the UN Security Council "expressed their deep concern at the prevailing insecurity ... and continued cross-border movements of armed elements, including militias and mercenaries".
Sylvie van den Wildenberg, spokeswoman for the UN mission known by its acronym UNOCI, said on Saturday it was reinforcing its force in the border area. "We have several thousand troops in the west, and we are reorganising in light of this incident," she said. "I can confirm that we are discussing with the authorities ways to increase security and protect civilians in the west. I cannot confirm any plan of a joint operation," she said.