South Sudan violence: What you need to know
Scores of people have died in fresh violence in South Sudan.
Here's everything you need to know about the world's newest country's past and the instability now threatening a peaceful future.
Where is South Sudan?
South Sudan, located in the centre of Africa, is the world's newest countries.
It voted overwhelmingly to break away from Sudan and became an independent country in 2011 after decades of civil war.
Years of violence have also left it as one of the least developed regions in the world - despite its reserves of oil.
Independence has failed to end the fighting.
Why is there tension?
In 2013, President Salva Kiir sacked his deputy Riek Machar, accusing him of launching a coup - an allegation Machar strongly refuted.
Kiir is from the Dinka, South Sudan's biggest ethnic group, while Machar is from the second largest group, the Nuer.
The country's army split into rival factions, with one half supporting Kiir and the other Machar.
Tens of thousands of people died during a bloody two-year civil war that was fought along ethnic lines.
A peace deal agreed last August ended the conflict.
But violence erupted again last Thursday when soldiers loyal to Kiir demanded to search vehicles of Machar supporters.
So has war started again?
Yes, according to a spokesperson for Machar, who told the BBC that the country was "back to war".
Machar's residence was attacked by forces loyal to Kiir, a spokesperson for the vice president said.
"Machar's residence was attacked twice today including using tanks and helicopter gunships," a spokesperson for Machar told Reuters.
Heavy gunfire was reported around the capital Juba.
UN officials said the fighting was now "relentless".
A health ministry source told Reuters on Sunday that at least 272 people had been killed, including 33 civilians.
What's being done to halt the violence?
UN Secretary-General Ban Ki-moon said on Friday the latest violence highlighted a lack of commitment to the peace process.
He urged the country's leaders to discipline military leaders and work together to implement the peace deal.
Kenya called on Kiir and Machar to resolve the latest crisis and to ensure heavy weaponry and soldiers were moved out of civilian areas.
Kenya Airways has suspended flights to Juba.
But there are growing fears South Sudan is sliding back into war again.