Last month, President Salva Kiir announced that elections would take place at the end of the transitional period in 2023.

But addressing members of his party in the capital Juba, Mr Machar said: "If you do not have unified forces, where will you get security for the elections?”

President Kiir and Mr Machar formed a unity government in February last year to end conflict between their rival forces and agreed to form a unified army of 83,000 troops.

Mr Machar listed three other conditions that he wanted fulfilled before elections could be held:

The return of millions of refugees from neighbouring countries
A nationwide census and
A permanent constitution because "we want free, fair and credible elections".
Civil war broke out in 2013 when Mr Kiir and Mr Machar fell out, leading to a conflict that has displaced some 4 million people.

South Sudan achieved its independence in 2011.