(CNN) -- Seven peacekeepers from Niger were killed Friday in an ambush in southwestern Ivory Coast, and more may be in danger, U.N. Secretary-General Ban Ki-moon said.
The blue-helmeted peacekeepers were part of the U.N. Operation in Cote d'Ivoire on patrol near the border with Liberia, where threats of attacks against civilians have prompted the operation to strengthen its presence, the United Nations said in a statement.
"These brave soldiers have died in the service of peace," Ban said. "I condemn this attack in the strongest possible terms."
The incident occurred near Para Village, a spokesperson for Ban said in a statement.
Ban called on the government of Ivory Coast "to do its utmost to identify the perpetrators and hold them accountable."
He added that he understood that other peacekeepers 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," he said.
A spokeswoman for the U.N. mission in Ivory Coast said Friday's incident was the first attack on peacekeepers since they entered the country in 2004.
Sylvie van den Wildenberg, in a telephone interview from her office in Abidjan, said the remaining forces were continuing to protect area residents, "who are living in a very difficult terrain -- their villages scattered."
Van den Wildenberg said it was not clear who was responsible for the attack, which occurred mid-afternoon. "This is an area where you have so many different types of armed people," she said. "People have different aims and different reasons to carry arms and to perpetrate attack. So this is a very complex environment. We can't extrapolate. We just can't fingerpoint any group."
The peacekeepers were on a reconnaissance patrol because U.N. officials had heard rumors several days earlier of armed men in the area threatening to attack a village, she said.
Van den Wildenberg said she had received reports that some Ivorian citizens may also have been killed or wounded, "but we are still checking the facts."
Because the shooting occurred in such a remote location, "it's going to take time for us to get the information."
U.N. peacekeepers remained in Ivory Coast after the 2010 presidential election, when the country was thrown into crisis after incumbent President Laurent Gbagbo refused to acknowledge defeat to former Prime Minister Alassane Ouattara. The latter was sworn in on May 21. Gbagbo is in custody at the Hague, accused of crimes against humanity during post-election violence that killed thousands.
In the statement, Ban's spokesperson said the secretary-general "remains seriously concerned about the continued instability in the border areas between Cote d'Ivoire and Liberia since the Ivorian post-elections crisis, which has resulted in the death of a number of individuals in that region."
According to the United Nations, its peacekeeping force in Ivory Coast as of April 30 included nearly 11,000 uniformed personnel, as well as several hundred international civilian personnel, local staff and volunteers. They provide technical, logistical and security support to the government.
CNN's Umaro Djau contributed to this report.