Seven United Nations peacekeepers were killed in an ambush in Ivory Coast on Friday while on patrol near the border with neighboring Liberia, the U.N. mission said.

“According to the provisional death toll, seven blue helmets were killed in an ambush ... seven blue helmets from Niger,” said Sylvie van den Wildenberg, spokewoman for the mission known by its acronym UNOCI.

It was not immediately clear who attacked the U.N. troops or if any Ivorian troops they were patrolling with were harmed.

The world’s top cocoa grower is gradually recovering from months of violence last year that followed a 2010 election.

The vote was won by Alssane Ouattara but incumbent Laurent Gbagbo refused to cede until defeated by French and U.N.-backed local forces who supported Ouattara.

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.

Van den Wildenberg said the mission had only recently increased its presence in the area, near the towns of Para and Tai, to boost efforts to protect civilians. The troops came under attack just a few kilometres from the border with Liberia.

Forty people have been killed in the surrounding villages in four cross-border raids since last July, according to HRW.