The government of Ivory Coast has promised to launch a manhunt for the attackers who killed eight civilians and seven United Nations peacekeepers.
The attack took place late Friday night in the country's southwest, according to a statement from the UN. "As per our information, at least eight civilians were killed, including a woman," Anouk Desgroseilliers, a spokeswoman for the UN Office for the Coordination of Humanitarian Affairs, told AFP news agency on Saturday.
She said that Friday's simultaneous raids on several villages near the town of Tai close to the Liberian border sparked an "immediate" exodus.
"Hundreds of people have arrived in Tai and one can imagine that thousands of others are on the road," she said. "Thirty-five families have crossed the border" into Liberia, she said.
The manhunt will involve troops from the Ivory Coast and Liberia, as well as UN forces. Paul Koffi Koffi, Ivory Coast's deputy defence minister, described them as "militiamen or mercenaries," and said the operation would start next week because his troops need time to prepare and gather equipment.
Ivory Coast's west is by far the most unstable part of the country and has been plagued by deadly attacks since a political and military crisis that started at the end of 2010 and left some 3,000 people dead throughout the country.
Earlier, the UN had only confirmed the deaths of the peacekeepers in the first attack of its kind in the country.
UN Secretary-General Ban Ki-moon said he was "outraged" by the killing and that more troops remained in danger.
"Even tonight, after the attack, more than 40 peacekeepers remain with the villagers in this remote region to protect them from this armed group," Ban told reporters.
The mission, called UNOCI, was started in 2003 in the midst of the country's years-long civil war. It saw extensive action following the presidential election in 2010, after the incumbent president, Laurent Gbagbo, proclaimed himself the winner.
It took months for forces loyal to the opposition candidate, Alassane Ouattara, to dislodge Gbagbo; UN troops fired on Gbagbo's troops and took control of the airport in the capital Abidjan during that time.
In a report published on Wednesday, Human Rights Watch said at least 40 people have been killed since July 2011 in raids the group blamed on fighters loyal to Gbagbo.
Gbagbo was captured on April 11, 2011 and has been in custody in The Hague since November on allegations of crimes against humanity.
UNOCI has about 11,000 troops, military observers and police in Ivory Coast. Up to Friday, 60 troops, 15 police, one military observer and 14 international and local civilian staff have been killed.