More than 150 soldiers died in fighting between South Sudan's army and former rebels in the capital Juba yesterday, a spokesman for the former rebels said.

"The number of casualties is over 150 killed," said Roman Nyarji, a spokesman for rebel leader turned Vice President Riek Machar, adding the combined death toll may rise further.

"We are expecting a bigger number of casualties because the two units of the presidential guard were all engaged yesterday," he said referring to bodyguard units of Mr Machar and his rival President Salva Kiir.

The violence came on the eve of the country's fifth anniversary of independence and represents another blow to a shaky peace deal that has so far failed to end a civil war that began in December 2013.

The shooting began when Mr Kiir and Mr Machar met at the presidential palace and initially involved their bodyguards.

The shootout, lasting about half an hour, quickly escalated from small-arms fire to heavier weapons and spread with machine-gun and artillery heard in several parts of Juba before subsiding after nightfall.

Mr Kiir and Mr Machar described yesterday's violence as "unfortunate".

By this morning a tense calm had fallen over the city with a heavy security presence but few civilians on the streets.