Forty bodies have been recovered from the River Nile, a medical organisation said Wednesday, bringing the death toll from a violent crackdown on protesters by security forces to around 100.
"They were taken with vehicles that belong to the Janjawid militias to an unknown destination," The Central Committee of Sudan Doctors (CCSD) said in a statement on Facebook.
The group had earlier placed the body count from Monday's violence at 60.
Meanwhile, Sudanese opposition groups rejected talks with the Transitional Military Council (TMC), hours after the interim leaders said they were ready to reopen negotiations.
"We don't see any way back into negotiations with the TMC," said Madani Abbas Madani, a spokesman of Forces of Freedom and Change (FFC), an opposition umbrella body.
Earlier on Wednesday, TMC leader Abdel Fattah Burhan said in a televised speech that the military council was "ready for negotiations with the other parties without any conditions."
The TMC decided to make this concession "to avoid our homeland slipping into chaos," he said, backtracking from Tuesday's announcement that there was no capacity for talks.
There is mounting international pressure to resolve the crisis, which started Monday when security forces fired live ammunition at a mass sit-in in front of military headquarters in the capital Khartoum.
More than 300 people were injured, according to the CCSD, although the exact number of wounded was difficult to establish since the TMC has switched off the internet in many parts of the country.
The developments in Sudan have raised "great concern" in Saudi Arabia, which called for dialogue to resume between the Sudanese parties to end the crisis.
"The Kingdom affirms the importance of resuming dialogue between the various parties in Sudan to fulfill the aspirations of the brotherly Sudanese people," the Saudi government said in a statement carried by the official SPA news agency.
Sudan is a partner to a military coalition led by Saudi Arabia and the United Arab Emirates fighting in Yemen against Houthi militia linked to Iran, a regional rival of Riyadh.
In April, Saudi Arabia and the UAE pledged to jointly offer 3 billion dollars in aid to Sudan, in a move aimed at supporting Sudan's interim military rulers in easing the country's economic woes.