A spokesman for the South Sudanese presidency and several government officials said they were not aware of the arrest.
“The employee is not abducted,’’ NRS spokeswoman Tuva Raanes Bogsnes told newsmen from Oslo.
However she confirmed that the employee was asked to come to the National Security on Thursday.
“Out of concern for our colleague we are not able to release any more information at this moment.
“NRC does not have any information about why he is being held. We expect that he is being treated well,’’ the NRC said in a statement.
However a spokesman for the South Sudanese presidency and several government officials said they were not aware of the arrest.
The NRC has been active in the region since 2004.
South Sudan, which became independent from Sudan in 2011, has been in the grip of a civil conflict since December 2013.
Tens of thousands have been killed and 3 million displaced.
The UN humanitarian coordinator for South Sudan recently expressed concern about bureaucratic impediments and access constraints to humanitarian agencies trying to assist people in need.