Sudan released dozens of opposition activists arrested last month in a crackdown on protests against rising food prices, an AFP correspondent reported.
The release of detainees, including some top opposition figures, came three days after the US embassy voiced concern over the arrests and said many of them were being held in "inhumane conditions".
Those released emerged from Kobar prison in northern Khartoum shouting "Freedom! Justice! Revolution!" the correspondent reported, after authorities had invited journalists to the scene.
They were greeted and hugged by family members who had been waiting outside for several hours.
"According to President Omar al-Bashir's order, all detainees are being released," Abdelrehman Al-Sadiq, a senior aide to Bashir, told reporters.
On Thursday, the US embassy said that "hundreds of political leaders, activists and ordinary citizens" were being detained by Sudanese authorities.
Many of the detainees were being "held in inhumane and degrading conditions, and without access to lawyers or family", the embassy said in a statement.
Freed detainees said they were expecting their release due to the political situation in the country.
"But we are still not fully free because several of our colleagues are still detained," said Al-Sidiq Al-Sadiq, son of former premier Sadiq al-Mahdi, whose government was ousted by Bashir in an Islamist-backed coup in 1989.
"The conditions that took us to jail have still not changed. There are still some laws that restrict freedoms."
During their detention, some prison officers had treated them well but "some did not", he said.
Those freed on Sunday included Fadlalla Burma Nasir and Sarah Nugdallah, senior leaders of Sudan's main opposition Umma Party, and women's rights activist Amal Habbani.
Sporadic protests have erupted since early January in Khartoum and some other parts of Sudan after the opposition and activists called for anti-government demonstrations to protest a surge in food prices.
Anti-riot police and security agents have so far swiftly managed to disperse the rallies.
Sudanese authorities are eager to prevent a repeat of deadly unrest that followed an earlier round of subsidy cuts in 2013.
Rights groups say dozens of people were killed when security forces crushed 2013 demonstrations, drawing international condemnation.