Sudanese police have quelled riots and imposed a curfew in Khartoum after anger at the death of ex-rebel leader John Garang spilled on to the streets.
Southern Sudanese hoped John Garang would change their lives
At least 20 people were reported dead in the clashes in the capital. There were also reports of unrest elsewhere.
Mr Garang, Sudan's newly appointed vice-president, died in a helicopter crash as he was returning from Uganda.
He signed a deal to end 21 years of civil war in January and was sworn in as deputy leader three weeks ago.
His former rebel group, the Sudan People's Liberation Movement (SPLM), has nominated deputy leader Salva Kiir as his successor and the next vice-president of Sudan.
The BBC's Jonah Fisher in Khartoum says that in choosing Mr Kiir, the SPLM has sent a clear message that there will be no radical departure from the Garang era.
US President George W Bush, UN Secretary General Kofi Annan and others joined Mr Kiir in urging the Sudanese people to remain calm and continue to implement the peace agreement.
Mr Garang's death was announced just before 0800 (0500 GMT) on Monday, though he had been reported missing over the weekend.
Our correspondent says gangs of youths from southern Sudan - Mr Garang's home - appeared on the streets, looting cars, throwing stones and smashing office windows.
Gunfire could be heard and there were clashes with security forces as they tried to seal off the city centre.
However, shortly after an overnight curfew was imposed at 1800 (1500 GMT), there was an eerie calm on the streets, our correspondent reports.
Mr Garang steered the SPLM rebels from the Christian and animist south through a war against the Islamic government in the north which left some 1.5m people dead.
Our correspondent says many of the 4m southern Sudanese living in Khartoum hoped Mr Garang would change their lives, and they are now venting their frustration at his death.
Mr Garang's death leaves a gaping hole in Sudan's political landscape, our correspondent says.
Three days of national mourning have been declared.
The news provoked grief in southern Sudan (picture: Mark Pearson)
The Ugandan presidential Mi-72 helicopter carrying Mr Garang back from a meeting with President Yoweri Museveni at his ranch in Rwakitura crashed in mountains near Mr Garang's base in New Site, southern Sudan.
Six of his associates and the seven-member crew also died in the crash, which has been blamed on bad weather.
Mr Garang had ruled the disparate SPLM with an iron hand, and managed to keep it together through years of fighting.
The conflict in Sudan ended with the signing of a peace agreement in January and Mr Garang became vice-president in a new government of national unity.
Sudan's President Omar al-Bashir said he was confident the peace agreement would remain on course.