Democratic Republic of Congo's Ebola outbreak is spreading at its fastest rate yet, eight months after it was first detected, the World Health Organization (WHO) said on Monday.

Each of the past two weeks has registered a record number of new cases, marking a sharp setback for efforts to respond to the second biggest outbreak ever, as militia violence and community resistance have impeded access to affected areas.

Less than three weeks ago, the WHO said the outbreak of the hemorrhagic fever was largely contained and could be stopped by September, noting that weekly case numbers had halved from earlier in the year to about 25.