The Government in Sudan says it has thwarted an attempted military coup.
"There has been a failed coup attempt, the people should confront it," state media reported on Tuesday.
Reports from the capital Khartoum and nearby Omdurman say there has been intense military activity, and the main bridge across the River Nile has been closed.
The plotters had tried to take over the state media building, AFP news agency reports.
The Government is reported to have said measures are being taken to contain the situation.
Video on social media appears to show armoured vehicles on city streets, and the AFP news agency reports that traffic now appears to be flowing smoothly in central Khartoum.
According to Reuters news agency, military spokesman Mohamed Al Faki Suleiman says the interrogation of suspects will soon begin.
Two years ago, President Omar al-Bashir, the country's long-term ruler, was toppled. A power-sharing agreement then established a government involving the military, civilian representatives and protest groups.
The BBC's Africa correspondent Catherine Byaruhanga says Sudan's transitional government is under pressure to deliver economic and political reforms amid competing demands from conservative and liberal constituencies.