Preparing to vote in South Sudan. (Photo Courtesy Tim McKulka)

An international conflict prevention think-tank says North and South Sudan must take political action to define their mutual border if they hope to avoid future complications and a return to conflict.

The International Crisis Group says the still undefined boundary line has hindered implementation of the 2005 Comprehensive Peace Agreement, and fuelled mistrust between its two signatory parties.

The accord called for the border between the North and the semi-autonomous South to be demarcated within six months but five years later, the task remains unfinished.

Zach Vertin, the ICG's Horn of Africa Analyst said both North and South should prioritise border demarcation despite being pressured by interest groups on either side.