At least 21 people have been killed after an aeroplane crashed in Sudan, a government spokesman has said.

Dominic Dim, southern Sudan's minister of defence was among those killed on Friday, Riek Mashar, the country's deputy prime minister said.

"The southern minister of defence and the former minister of cabinet affairs were on the plane along with other passengers from an SPLM conference on their way back to Juba," said Deng Goc, an SPLM spokesman.