The army of north Sudan has demobilized 15,000 southerners ahead of the south's declaration of independence on Saturday.
A dismissal ceremony took place in Khartoum Thursday.
The north and south are trying to disentangle themselves before the new Republic of South Sudan becomes a country, but the sides have yet to resolve issues on borders and oil revenue.
The north's army is currently fighting pro-southern elements in the northern-controlled state of Southern Kordofan.
Meanwhile, the United Nations Security Council is expected to vote Friday on a resolution to create a peacekeeping mission for South Sudan with 7,000 military personnel and 900 international police.
In other developments, authorities have closed streets in the south's capital Juba so organizers can prepare for Saturday's independence ceremony.
Some 30 African heads of state are expected to attend, including Sudanese President Omar al-Bashir, and U.N. Secretary-General Ban Ki-moon.
Mr. Ban said called Thursday for a smooth secession and an immediate ends to clashes in Southern Kordofan.
North and south Sudan fought a 21-year civil war that ended in 2005. Southern Sudan voted overwhelmingly to split from the north in a January referendum.