At least five Sudanese protesters and a member of the security forces have died in clashes in the capital, Khartoum.
They were killed in gunfire at a sit-in outside military HQ where demonstrators are demanding full civilian government. Dozens have also been injured.
Protesters said soldiers were responsible, but the army blamed it on “unidentified elements”.
Sudan has been ruled by a transitional military council since last month’s toppling of President Omar al-Bashir.
It is unclear exactly what happened but activists have been talking about how they were targeted by a gunman.
“He shot a bullet at me, he was 20 metres away from me, at most,” Raed Mubarak told the Reuters news agency.
The US embassy in Khartoum has said actions by the military council resulted in the violence.
“The tragic attacks on protesters yesterday… were clearly the result of the Transitional Military Council (TMC) trying to impose its will on the protesters by attempting to remove roadblocks,” it said on its Facebook page.
“The decision for security forces to escalate the use of force… led directly to the unacceptable violence later in the day that the TMC was unable to control.”