Ebola-hit Guinea and Sierra Leone saw a spike in new cases last week, the World Health Organization (WHO) said Wednesday, dashing hopes that the deadly outbreak was petering out.

The seven days ending Sunday "saw the highest weekly total of confirmed cases of Ebola virus disease for over a month," the UN health body said in its latest update.

A full 35 new cases were reported during the week in Guinea and Sierra Leone, up from just nine a week earlier.

According to the latest figures, the outbreak has now infected a total of 26,933 people and killed 11,120, mainly in Guinea, Sierra Leone and neighbouring Liberia, which was declared Ebola-free on May 9.