The Ceasefire and Transitional Security Arrangement Monitoring Mechanism says its team leader has been detained in Torit.
Its communication office said in a statement that the incident happened at approximately 8.45am this morning.
CTSAMM said this is one in a series of such restrictions on freedom of its movement.
It called on the Transitional Government to ensure the immediate release of the Monitoring and Verification Team Leader to enable its focus on discharging its mandate and persevere in its pursuit of peace.
Authorities in Torit, Imatong State, were not available for a comment.