Clashes between herders and fishermen in northern Cameroon have killed at least 32 people this month, with 19 villages torched, the UN High Commissioner for Refugee said on Thursday.

Some 11,000 people fled to Chad and a further 7,300 were displaced in Cameroon’s Far North after fighting broke out on Aug. 10 between Choa Arab 

herders and Mousgoum fishermen and farmers, the UNHCR said.

Officials described the fighting as Cameroon’s worst ethnic violence in years.

The herders were angry because their livestock was falling into holes dug by fishermen to capture fish in pools of receding floodwaters, according to a local official.

The refugees in Chad were in urgent need of shelter, UNHCR said, with many sleeping under trees.

“(UNHCR) calls on the governments concerned to do everything possible to reduce the intercommunal tensions that have caused this displacement and to ensure the safety of people forced to flee,” said Millicent Mutuli, a regional director of UNHCR.

The ethnic violence further complicates security in a region where Cameroon’s army has been battling Boko Haram for years and, more recently, militants linked to Islamic State.