The US assistant secretary of state for Africa, Tibor Nagy, has called for a credible and independent investigation into the killing of dozens of protesters by security forces in Sudan last week, calling it "critically important".
There has been international condemnation of Sudan's Transitional Military Council (TMC), which decided last week to scrap all existing agreements with the main opposition coalition and announced plans to hold elections within nine months.
Before that point, the military and protesters agreed a three-year transition period to civilian rule.
On Thursday, Mr Nagy met senior members of the TMC for talks in the capital, Khartoum.
He described the discussions "as frank [and] as direct as possible, and obviously we didn’t agree on some points".
Speaking to reporters in the Ethiopian capital on Friday, he said the US wants to see a civilian government acceptable to the Sudanese people at the end of the transitional period.
A third-party negitiator would help to break the deadlock between the military council and the opposition, Mr Nagy said.
He applauded efforts by the African Union and Ethiopia's prime minister to broker a deal, but added that "all tools are available and remain on the table".