The release, confirmed by the International Committee of the Red Cross, coincided with a surge of violence in Darfur, after the rebel Justice and Equality Movement (JEM) suspended its participation in peace talks.
JEM told Reuters this week that it had grabbed the soldiers during almost "continuous" clashes with Sudan's army in central and southern Darfur. "We handed over 35 prisoners of war in south Darfur. Nine of them are injured," senior JEM official Al-Tahir Al-Feki told Reuters.
Before the release was announced, a spokesman for Sudan's army said there had been a number of clashes as it tried to stop JEM building up its forces in central Darfur, but added they were mostly small confrontations.
Darfur's joint UN/African Union UNAMID peacekeeping force said almost 600 people died in rebel and tribal clashes in May, the bloodiest month for more than two years.
The force added it was investigating reports an unknown number of people had died in clashes between the rival Misseriya and Rizeigat tribes in the Kass area of south Darfur on Monday.
The Red Cross said it took the captives from JEM and transferred them to the army in Nyala, capital of South Darfur state, on Wednesday.
The United Nations' World Food Program said Sudanese authorities had grounded most flights to remote locations in south Darfur as a security precaution, leaving thousands of people stranded without aid.
JEM was one of two mostly non-Arab rebel groups that took up arms against the Khartoum government in 2003, accusing it of neglecting the region.
