At least 115 soldiers have been killed in heavy fighting in South Sudan on the anniversary of the country’s fifth year of independence.

The outburst of violence has thrown a fragile peace into jeopardy – a peace agreement ending a two year civil war was only negotiated in August 2015.

British nationals have been advised to leave the country and non-essential embassy staff are being withdrawn.

“South Sudan today marked the most horrifying Independence Day in the world this year,” said government official James Gatdet Dak on Facebook.

Another resident, Buay Joshua De Kapduel, wrote simply: "Unhappy 5th Independence Day".

Clashes between the forces of former rivals President Salva Kiir and vice president Riek Machar began for unknown reasons on Thursday and continued on Friday. Gunfire erupted near the presidential residence in the capital, Juba, where the leaders were meeting for talks. Witnesses later reported seeing corpses on the lawn.

Both leaders said they did not know what had triggered the fighting between their factions and called for calm.

William Gatjiath Deng, spokesman for Mr Machar's military faction, said the fighting had occurred near the state house and in army barracks.

"In the morning we collected and counted 35 [dead] from the SPLM-IO (Machar's faction) and 80 people from the government forces," he said.

Deng said the death toll could rise on the side of Mr Machar "because there are some soldiers seriously wounded".

The government side had no immediate comment on the situation.

The fighting was not restricted to Juba and also hit a UN compound south west of the city. Fighters reportedly waited until women and children went into the base to fire on it.

Unicef has condemned the violence and in a statement said it is “deeply alarmed” by the news. “Children and their families in South Sudan have suffered enough from violence, displacement and killings in this brutal conflict. It is time that peace becomes more than agreements on paper, but a reality for those who are most vulnerable,” said Unicef's Regional Director for Eastern and Southern Africa, Leila Pakkala.

Thursday and Friday's gunfights were the first major outbreak of violence in the capital since Mr Machar returned to the capital in April after his re-appointment as vice president.

Witnesses said Juba was calm but tense on Saturday, with road blocks mounted on some streets. Heavy military vehicles could be seen patrolling and most businesses were closed.

"It seems as though things have certainly calmed from what they were last night. However the situation is still very, very tense," said Jeremiah Young, an aid worker with World Vision.

Mr Young said there was a chance the security situation could "deteriorate very quickly due to the tensions within Juba and the surrounding areas."

On Saturday, the Foreign and Commonwealth Office advised British nationals in South Sudan: "If you have no pressing need to remain, you should consider leaving by commercial means, if it is safe to do so. If safe passage to the airport is not available then we advise all British nationals in Juba to remain inside."

Vehicles belonging to the US embassy shot at by government forces on Thursday night, CNN reported. However, no one was hurt and State Department spokesman John Kirby said he believed the vehicles were not intentionally targeted.

Africa's newest nation is emerging from a two-year civil war which started in December 2013 after Mr Kiir sacked Mr Machar as vice president.

The conflict was largely fought along ethnic lines with Mr Kiir mostly drawing support from his Dinka tribe while Mr Machar was backed by his Nuer tribe.