"Eight wounded from live bullets so far," Amjad Farid, a spokesman for the umbrella protest group the Alliance for Freedom and Change wrote on Facebook.
A witness told AFP that gunshots had been fired near the protest camp outside the army headquarters in central Khartoum.
"There are gunshots in Nile Street and around the sit-in and we are seeing several wounded," said Mohamed Dahab, a volunteer at a field clinic at the protest camp.
A protest leader also said on condition of anonymity that among the eight wounded, three were in serious condition.
The latest violence comes hours ahead of crucial talks between Sudan's ruling military council and protest leaders, aimed at finalising the make-up of a new body to govern for a three-year transition period.