A US envoy for Africa on Friday called for an "independent and credible" investigation into 3 June's evacuation by security forces of a sit-in outside the Ministry of Defence headquarters in Khartoum that resulted in tens killed and injured.
"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 from Addis Ababa after a two-day visit to Khartoum.
Nagy said "Until June 3rd, everybody was so optimistic. Events were moving forward in such a favourable direction after 35 years of tragedy for Sudan."
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 by the army in April of this year following mass protests against his 30-year-old rule.
Following Bashir's ouster, protesters carried on with a sit-in outside Khartoum defence ministry headquarters to demand a transition to civilian rule.
On Thursday, a spokesman for the Transitional Military Council (TMC) which replaced Bashir expressed regret over the events of 3 June, saying the plan had been to clear an area close to the sit-in but "excesses happened."
The TMC rejected an international investigation, saying it was carrying out its own probe, whose findings would be released on Saturday.