Efforts to stamp out West Africa's Ebola epidemic are being thwarted by villagers touching and washing the infectious bodies of dead victims at secret burials and difficulty in tracing those exposed to the virus, U.N. officials said on Thursday.

The number of new cases rose for the first time this year in the past week, coinciding with a looming funding shortfall and the approach of the rainy season that will hamper aid efforts from April, they warned.

"The commonest way in which people are getting Ebola is through the rituals that take place when somebody is buried, particularly the important cleansing and touching that goes on," Dr. David Nabarro, U.N. Ebola special envoy, told a briefing.