More foreign health workers are needed to help tackle the Ebola epidemic, which is spreading quickly in western Sierra Leone and deep in the forested interior of Guinea, a senior U.N. official said on Tuesday.

The death toll from the Ebola outbreak in West Africa has risen to 6,331 in the three worst hit countries, with Sierra Leone overtaking Liberia as the country with the highest number of cases, the World Health Organization says. "We know the outbreak is still flaming strongly in western Sierra Leone and some parts of the interior of Guinea. We can't rest, we have to still push on," said David Nabarro, the U.N. Special Envoy on Ebola.

More treatment centres are opening in Sierra Leone but they need additional trained staff, he told a news briefing. "We don't yet have the full number of functioning treatment centres and places where people who are ill can be kept away from others," he said.

"We are anticipating several hundred beds to come on stream in the next few weeks, and that will lead to the situation calming down." The deadly virus is spreading especially in Sierra Leone's capital Freetown and Port Loko, where a more intense response is needed, said Nabarro, a veteran public health expert. "Although I hate predictions, I am at least confident that unless something goes radically wrong we will see an improvement there (in Freetown). It's a bit like what Monrovia was like 4 to 6 weeks ago and I think that it will certainly calm down."

The rise in the spread of Ebola in western Sierra Leone reflects the fact that tribal-led communities have yet to fully accept the outbreak and take action to avoid infection, he said. "There are reports coming through of places where people who are sick, staying at home and perhaps infecting their families."

The second "particularly troublesome" area is the northern part of Guinea's interior, a region known as Guinea Forestiere where the epidemic began nearly a year ago, Nabarro said. "We have been working very closely with Mali to try to make sure if cases perchance cross the border that they can be dealt with very quickly."

Mali has reported eight Ebola cases, six fatal, to date.

(dna)