The soldiers' release, which occurred on Wednesday, followed a request by the parties to the conflict, the International Committee of the Red Cross (ICRC) said.
"We stand ready to act as a neutral intermediary for the release of detainees from all side to the conflict whenever requested," Jean-Christophe Sandoz, ICRC's head of delegation in Sudan, said in a statement.
The three Sudan cities that make up the wider capital around the confluence of the River Nile - Khartoum, Bahri and Omdurman - have seen more than 10 weeks of heavy clashes and looting, while the conflict has triggered a resurgence of ethnically motivated killings in the western region of Darfur.
Residents and news reports said fighting had intensified in Omdurman on Wednesday afternoon. The Darfur Bar Association, an activist group that monitors the conflict, said the Rapid Support Forces (RSF) fighting the Sudan army had carried out lethal attacks in the Manwashi area of South Darfur State twice in the past five days.
The United Nations mission in Sudan urged the two sides to maintain the truces they had committed to.
The RSF and allied militias remained accountable for violence, rape and looting in areas it controlled, and for ethnically targeted violence in Darfur, while the army remained accountable for attacks and aerial bombardments in residential areas, the mission said in a statement.
"These parties should be reminded that the world is watching and accountability for crimes committed during wartime will be pursued," the statement said.
War between Sudan's army and the RSF has caused a major humanitarian crisis and displaced nearly 2.8 million people, of which almost 650,000 have fled to neighbouring countries.
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