South Sudan won its independence in 2011 but has been torn by a civil war for the past year, with troops loyal to President Salva Kiir fighting forces of former vice president Riek Machar.
Tens of thousands of people have died and some two million have been displaced, according to the UN. The conflict has taken on a bitter ethnic dimension, with the Dinka people of Kiir fighting the Nuer of rebel chief Machar.
Here is a chronology of the fighting.

-- DECEMBER 2013 --
- 15: Heavy gunfire erupts in Juba, where tensions rose after Machar was fired as vice-president in July. Kiir denounces a coup and says Machar is behind it.
Machar later denies this and accuses Kiir of starting the war by launching a purge of his rivals. The fighting spreads to several states.

--JANUARY 2014--
- 10-20: Government troops recapture the northern city of Bentiu, capital of oil-rich Unity State, Malakal, capital of Upper Nile, and Bor, capital of Jonglei. The towns are left in ruins.
Uganda sends troops to reinforce the South Sudanese army.
- 23: Government and rebels sign a ceasefire deal but, like several subsequent pacts, it is swiftly broken.

--FEBRUARY--
- 27: Human Rights Watch says war crimes have been committed by all sides.
In March, the African Union launches a probe to identify those responsible for atrocities since the conflict began.

--APRIL--
- 15: Rebels wrest back control of Bentiu and issue an ultimatum to oil companies to shut down production. A few days later the UN accuses rebels of massacring "hundreds" of civilians.
- 17: At least 58 people die in an attack by hundreds of armed men on a UN base in Bor sheltering thousands of civilians.

-- MAY --
- 2: US Secretary of State John Kerry visits Juba, threatening both sides with sanctions and warning of the risk of "genocide". Four days later, the US slaps sanctions on two military commanders from both sides.
- 27: A Security Council decision refocuses the United Nations Mission in South Sudan (UNMISS) on civil protection tasks.

-- JULY --
- 10: The European Union hits South Sudanese rebel chief Peter Gadet and government army officer Santino Deng with a travel ban and asset freeze for their role in reported atrocities.

-- AUGUST --
- 19: Fighting flares around Bentiu despite the threat of UN sanctions.
- 26: Three people die and one is injured when a UN helicopter is shot down near Bentiu. Each side blames the other.

-- OCTOBER --
- 20: Kiir and Machar accept mutual responsibility for the civil war, but peace talks remain blocked and the ceasefire agreement is broken repeatedly.
At the end of the month, fresh fighting erupts in Bentiu after several months of relative calm.

-- NOVEMBER --
- 8: East Africa's regional bloc IGAD gives both sides two weeks to finalise a power sharing deal, and threatens to approve more sanctions and possibly a military intervention. The deadline is ignored.
Fighting erupts in several states however, after the latest talks between Kiir and Machar fail.
In mid-November, the International Crisis Group says at least 50,000 people have been killed by the fighting. Diplomats suggest the number could be double that.