An international medical official with the U.N. Mission in Liberia has tested positive for the Ebola virus and is receiving treatment, the U.N. said on Wednesday.

The official, who was not identified, is the second member of the mission, known as UNMIL, to contract Ebola. The first died on Sept. 25.

The world's worst outbreak of Ebola has killed more than 3,400 people, predominantly in Liberia, Guinea and Sierra Leone.

The staff member reported having symptoms to UNMIL medics on Sunday, a statement said.

"The UNMIL Medical team has conducted immediate and robust contact tracing to ensure all people that came into contact with both staff members while they were symptomatic are assessed and quarantined," it said.

All staff members considered at-risk have been isolated and ambulances and other locations have been decontaminated.

Liberia has suffered 2,210 deaths from Ebola as of Oct 4, the government said, adding 212 to the death toll since a previous update published by the World Health Organization, which gave figures as of Sept 28.