A US envoy for Africa on Friday called for an "independent and credible" investigation into last week's crackdown on protesters in Sudan that left dozens of dead.
"The USA believe very strongly there has to be an investigation which is independent and credible which will hold accountable those committing the egregious events," Tibor Nagy, the assistant secretary of state for Africa, said in Addis Ababa after a two-day visit to Khartoum.
Thousands of protesters who had camped outside the army headquarters in central Khartoum for weeks were dispersed on June 3.
According to doctors linked to the protest movement, 120 people died and hundreds were wounded, while Sudan's health ministry put the death toll at 61.
Nagy said the crackdown marked a brutal reversal in a situation where hope had flowered.
"The events of June 3rd constituted, in our point of view, a 180-degree turn in the way events were going, with murder, rape, by members of the security forces," he said in a conference call with journalists.
"Until June 3rd, everybody was so optimistic. Events were moving forward in such a favourable direction after 35 years of tragedy for Sudan".
Nagy -- the US ambassador to Ethiopia between 1992 and 2002 -- pointed to fears in the region about potential chaos in Sudan.
"The last thing Egypt wants is another Libya on its southern border. The last thing Ethiopia wants is another Somalia on its northwestern border," he said.
Sudanese opposition leader Sadiq al-Mahdi earlier Friday called for an "objective" international investigation.
Mahdi's elected government was toppled in 1989, in an Islamist-backed coup led by Omar al-Bashir.
After three decades in power, Bashir was himself ousted in April following mass protests, backed by Mahdi.
Bashir was replaced by a military council, but protesters carried on with a sit-in outside Khartoum military headquarters to demand a transition to civilian rule.
Nagy said the US backed mediation efforts by the African Union and an eight-country regional bloc, the Intergovernmental Authority on Development (IGAD), which is currently chaired by Ethiopian Prime Minister Abiy Ahmed.
"The USA seek a civilian-led government at the end of this transition which is acceptable to the Sudanese people," he said.
On Thursday, a spokesman for the military council expressed "regret" over the events of June 3, saying the plan had been to clear an area close to the sit-in but "excesses happened".
The council rejected an international investigation, saying it was carrying out its own probe, whose findings would be released on Saturday.
Separately, the head of the military council, General Abdel Fattah Burhan, who met Nagy in Khartoum, made a one-day visit to Eritrea, the Eritrean ministry of information said on its website.
He met President Isaias Afwerki, who "underlined the need for all Sudanese political forces and population to participate in the perceptive transition phase the country is facing," the ministry said.