The UN World Food Program has reiterated its concern about the safety of one of its workers who was abducted by gunmen a month ago in Upper Nile State.

WFP says Mark Diang was taken at gunpoint by men in plain clothes at Malakal airport on the 16^th of October.

It says it has not received any information on the whereabouts of Mark Diang since he was abducted.

Country Director Joyce Luma says WFP is gravely worried about the safety of its staff and calls for his to release him unharmed.

WFP has called upon South Sudanese authorities to facilitate his release and bring those responsible for his disappearance to justice.

It says many of its aid workers in South Sudan now fear for their own lives as they provide needed supplies to the people.

In a statement, WFP says it is re-assessing its security arrangements in parts of South Sudan, to ensure that its staff can operate safely.

It says this requires temporarily restricting operations in some areas while seeking renewed security assurances from authorities for emergency teams to deliver food assistance to communities isolated by conflict.