The head of the U.N. peacekeeping mission in Ivory Coast condemned the attack as "a severe violation of international law."
The U.N. Security Council established the peacekeeping mission in 2004, two years after civil war broke out in Ivory Coast. The mission's mandate is to expire July 31.
Secretary-General Ban Ki-moon condemned the attack and called on the Ivory Coast government to "do its utmost to identify the perpetrators and hold them accountable for this wanton attack," the Los Angeles Times reported.
Citing unconfirmed reports, Ban said an undetermined number of civilians were killed in the ambush.
A former Ivory Coast minister was extradited from Togo after authorities found evidence he was working to create turmoil at home, an official said.
Authorities in Togo returned Moise Lida Kouassi to Ivoirian custody. He served as defense minister in 2002 and remained a key ally to former President Laurent Gbagbo following a 2010 election crisis that threatened to push Ivory Coast back into civil war.
Ivoirian Interior Minister Hamed Bakayoko said Kouassi had broken the terms of his exile in Togo.
"He broke this duty to keep quiet on several occasions," Bakayoko was quoted by the BBC as saying. "He was found to have compromising documents which implicate him in projects to destabilize Ivory Coast."
Ggabgo is awaiting trial at the International Criminal Court on charges of committing crimes against humanity during the post-election conflict. Human rights groups allege that both sides likely committed atrocities during the crisis.