More than 3 000 protesters took to the streets of the Sudanese capital Khartoum to demand President Omar Hassan al-Bashir quit.
Khartoum's gaping revenue hole has worsened the distrust between the north and south.
Denel Mechem says it is working closely with international and Sudanese authorities to ensure the safe release of South African employee Thabo Siave.
Sudanese planes have launched a bombing attack on the South Sudanese town of Bentiu, after Khartoum called off peace talks amid claims of incursion.
South Sudan has accused Sudan of launching fresh attacks along their disputed border, stalling peace talks in Addis Ababa.
South Sudan has ordered oil companies to shut down oil production within two weeks, to prevent Sudan from stealing more oil from the new country.
South Sudan, now an independent state, is facing a rise in conflict between militia groups which threaten the lives of civilians, a UN official says.
At least 59 soldiers and militiamen were killed and dozens wounded on Thursday in clashes between the South Sudan army and local militia groups.
The United States said on Monday it will recognise South Sudan as the world's newest nation as it moved to taking the north off a terrorism blacklist.
Turnout at south Sudan's independence referendum has defied gloomy expectations and is almost guaranteed to reach the 60% needed for a valid poll.
Sudan's President Omar al-Bashir pledged on Tuesday to help build a secure, stable and brotherly state in the south if it votes for independence.
A Sudanese court on Wednesday convicted eight models who took part in a mixed-gender fashion show with "indecency" and ordered them to pay a fine.
Aid workers in South Sudan have criticised the government for not helping with the influx of citizens hoping to vote from the north.
The south Sudanese army accused the north's troops of provoking it, with the intention of breaking a ceasefire agreement between the two.
The United States has offered to remove Sudan from its terror list early to keep a January referendum that may partition the country on track.
Sudan on Wednesday denied trying to import arms on a ship intercepted in Cyprus, saying explosives on board had been ordered by a mining company.
Darfur rebels on Wednesday condemned a death sentence on two of its members by a Khartoum court, saying it endangered the peace process.
Election observers in Sudan said on Friday they were gravely concerned about government crackdowns on opposition rallies.
A Sudanese Christian teenager has been lashed 50 times for wearing what a judge considered an "indecent" knee-length skirt.
The Permanent Court of Arbitration in The Hague on Wednesday moved the borders of Sudan's Abyei region.