Liberia's United Nations peacekeeping mission says 41 staff members, including 20 military personnel, are under "close medical observation" after an international member of its medical team contracted Ebola.

The mission said in a statement that the measures were precautionary and that none of the staff members had shown signs of Ebola.

The staffers were identified via contact tracing and will be observed for 21 days, which the World Health Organisation says is the maximum incubation period.

The member of the medical team, whose name and nationality have not been disclosed, was diagnosed Monday and arrived in Germany Thursday for treatment - the third Ebola patient to be flown there.

It is the second case of a UN staffer contracting Ebola in Liberia. The first died on September 26.