Khartoum - Sudanese forces entered the site of a sit-in in central Khartoum early on Monday amid gunfire, witnesses and Arab television stations said, in what activists described as an attempt to disperse protesters demanding civilian rule.
A medical association affiliated to protesters said at least two people were killed and dozens injured in the raid, which was still in progress.
"The protesters holding a sit-in in front of the army general command are facing a massacre in a treacherous attempt to disperse the protest," the main protest group said in a statement, urging the Sudanese people to come to their aid.
The violence comes amid a persistent deadlock in talks between protesters and Sudan's military rulers over demands to hand over power to civilians.
The Transitional Military Council (TMC), which assumed power in April when the military ousted President Omar al-Bashir after three decades in office, has offered to let protesters form a government to run the country but insists on maintaining overall authority during an interim period.