GENEVA — West Africa’s deadly Ebola epidemic is probably much worse than the world realizes, with health centers on the front lines warning that the actual numbers of deaths and illnesses are significantly higher than the official estimates, the World Health Organization said.

So far, 2,127 cases of the disease and 1,145 deaths have been reported in four nations — Guinea, Liberia, Nigeria and Sierra Leone — the W.H.O announced Friday. But the organization has also warned that the actual number is almost certainly higher, perhaps by a very considerable margin.

“Staff at the outbreak sites see evidence that the numbers of reported cases and deaths vastly underestimate the magnitude of the outbreak,” the group said in a statement on Thursday.