South Sudan's leader Salva Kiir has in a shock move dismissed one of his vice-presidents, Benjamin Bol Mel, who had been tipped as his possible successor.

Kiir stripped Bol Mel of his military rank of general and dismissed him from the national security service. He also sacked the central bank governor and the head of the revenue authority, both considered close allies of Bol Mel.

No explanation was given for the dismissals, which were announced in a decree broadcast on state television.

It comes when there are growing fears of political instability and a possible return to civil war, after the recent collapse of a fragile power-sharing agreement between Kiir and opposition leader Riek Machar.

Bol Mel, 47, was only appointed vice-president in February, replacing James Wani Igga, a veteran politician and general.

He was also elevated to become the first deputy chairman of the ruling SPLM party, which analysts believe gave him more powers and positioned him as a potential successor to the 74-year-old Kiir. The president later promoted him to the full rank of a general in the National Security Service (NSS).

Bol Mel's promotion came despite the US placing sanctions against him for alleged corruption in 2017, which were renewed earlier this year. The US Treasury described Bol Mel as Kiir's "principal financial advisor". Kiir's office denied the description.

Bol Mel has never directly responded to the corruption accusations against him and has not commented on his sacking. (BBC)