A United Nations spokesman says at least seven peacekeepers from Niger have been killed in an ambush in western Ivory Coast, near the border with Liberia.

In a statement, U.N.'s special envoy for Ivory Coast , Bert Koenders, strongly condemned the deadly ambush Friday against the peacekeepers, describing it as a “very serious violation of international law.”

The soldiers were part of a patrol that was on a mission south of the town of Tai, in an area where the U.N. recently strengthened its presence due to threats of attacks against the civilian population.

It is not clear who attacked the patrol.

Koenders said the U.N. will take all the required measures following, what he called, ” this severe violation of international law.”

Ivory Coast is recovering from last year's violence following a contested 2010 election.

Human Rights Watch warned earlier this week that fighters loyal to Ivory Coast's former president Laurent Gbagbo staged attacks on Ivory Coast from Liberia. It said that about 40 people have been killed in several cross-border raids since last July.

Mr. Gbagbo was captured in April of last year and has been in custody in The Hague since November on allegations of crimes against humanity while fighting to prevent election winner, current Ivorian President Alassane Ouattara, to take power.