The U.N. Ebola Emergency Response Mission will not fully meet its Dec. 1 target for containing the virus due to escalating numbers of cases in Sierra Leone, Anthony Banbury, the head of UNMEER, said on Monday.

The mission set the goal in September of having 70 percent of Ebola patients under treatment and 70 percent of victims safely buried. That target will be achieved in some areas, Banbury told Reuters, citing progress in Liberia.

"We are going to exceed the Dec 1 targets in some areas. But we are almost certainly going to fall short in others. In both those cases, we will adjust to what the circumstances are on the ground," he said in an interview.

The death toll in the worst Ebola epidemic on record has risen to 5,459 out of 15,351 cases identified in eight countries by Nov. 18, the World Health Organization said on Friday. Almost all those cases are in Guinea, Sierra Leone and Liberia.

Banbury said the areas of greatest concern are in rural parts of Sierra Leone as well as the city of Makeni in the center of the country and Port Loko in the northwest and the capital Freetown.

To combat rural cases, health workers need to deploy rapid response units complete with specialists and equipment that can be flown by helicopter to remote villages at the first sign of the disease's spread, he said.

UNMEER was set up to provide coordination, policy and logistics rather than to treat patients. It needs more resources to halt Ebola as quickly as possible but the emphasis now is on allocating existing resources in the smartest way, he said.

"Earlier decisions about the need for rapid construction of large ETU's (Ebola Treatment Centres) were taken in a certain context where that's what made sense .... Those efforts were to a large degree successful. But in the meantime the disease has spread," he said.

He said surveillance to prevent further cross-border spread of Ebola must be also improved, given the transmission from Guinea into Mali, where at least six people have died.

U.S. Brigadier General Frank Tate, deputy commanding general of U.S forces helping Liberia fight Ebola said on Monday there is a dramatic improvement in the country worst-hit by the outbreak.