DAKAR, Senegal (AP) — Dozens are feared dead after a boat carrying migrants sank off Mauritania’s coast, according to the U.N. Refugee Agency.

Approximately 40 people were on board the vessel that sank off the coast of Nouadhibou, Mauritania, U.N. Refugee Agency Special Envoy for the Central Mediterranean Vincent Cochetel said on Twitter Thursday.

There is one survivor from Guinea, he said. Further details were not yet available.

“UNHCR & IOM along with authorities & partners are trying to step up efforts to prevent such tragedies, but traffickers keep lying to their clients,” Cochetel wrote in the tweet.

Those aboard the vessel were migrants from sub-Saharan Africa, confirmed U.N. Refugee Agency Africa spokesman Charlie Yaxley. U.N. officials are at the site providing assistance, he said.