The number of new cases of Ebola rose in all three of West Africa's worst-hit countries last week, the World Health Organization said Wednesday, ending several weeks of encouraging declines across the region.

Suspicion of aid workers, especially in Guinea, and unsafe local practices were continuing to hamper efforts to halt the deadly virus, the United Nations agency said.

"An unsafe burial that took place in early January in the (Guinean) eastern prefecture of Lola, on the border with Cote d'Ivoire, has so far resulted in an outbreak of 11 confirmed cases," it said.