DOUALA, Aug 12 (Reuters) - Clashes between herders and fishers in northern Cameroon have killed at least 12 people this week in the area"s worst ethnic violence in recent memory, local officials said on Thursday. The fighting in the Far North region, already plagued by violence from Islamist militant group Boko Haram, broke out on Tuesday, with fishers from the Mousgoum ethnic group opposing Arab herders, said Mahamat Bahar, a local customary chief. The herders were angry because their livestock were falling into holes in the ground dug by the fishers to lure their catch, Bahar told Reuters. He said many people had died but did not provide an exact number. Cherif Mahamat, another local official, said at least 12 people had died. Another official, who asked not to be named, said the provisional death toll stood at 14. "This is the biggest ethnic attack I have ever seen," Mahamat told Reuters. "Right now, there are fires burning in other villages." The ethnic violence is a worrying development in northern Cameroon, where the army has for years been battling Boko Haram and, more recently, militants linked to Islamic State. In nearby countries like Mali and Niger, Islamist militants affiliated with Islamic State and al Qaeda have exploited ethnic conflicts to win recruits and undermine confidence in state authorities. Bahar said one of the reasons the violence was so deadly was that the presence of Boko Haram and bandits in the area had led local residents to acquire firearms to protect themselves. "The agro-pastoral conflict between farmers and herders and fishers and herders has always existed. But this is the first time it is at such a scale," Bahar said.