South Sudan quashes coup attempt, says President Kiir
South Sudan's President Salva Kiir says an attempted coup by soldiers loyal to his former deputy Riek Machar has been put down.
Mr Kiir said the government was in full control of the capital, Juba, after a night of heavy fighting between soldiers in the presidential guard.
A night time curfew has been put in place and a number of arrests have reportedly been made.
Several people were reported injured and hundreds have fled to a US base.
Hilde Johnson, the UN's special representative in the country, said she was "deeply concerned" and urged "all parties in the fighting to cease hostilities immediately and exercise restraint".
"I have been in touch regularly with the key leaders, including at the highest levels to call for calm," she said.
The fighting in Juba broke out overnight, and intensified in the early morning, with reports of continuous gunfire and several explosions.
The city's airport has been closed and the state TV channel SSTV went off air for several hours.
Shortly after it came back on air, SSTV broadcast an address from Mr Kiir, wearing military uniform rather than his usual civilian clothing and flanked by government officials.
He said the violence "was an attempted coup", but that the government was now in full control and the attackers were being chased down.
He said the fighting began when unidentified uniformed personnel opened fire at a meeting of SPLM, followed by an attack on army headquarters near the university carried out "by a group of soldiers allied to the former vice-president Dr Riek Machar and his group".
"I will not allow or tolerate such incidents once again in our new nation. I strongly condemn these criminal actions in the strongest terms possible," he said, vowing those responsible would be have to stand "before the appropriate law institution".
The ruling party, former rebel force the Sudan People's Liberation Movement (SPLM), would never allow power to be transferred by force, he said.
He announced a curfew would be in place every night between 18:00 and 06:00, beginning on Monday.
"Rest assured that the government is doing all it can to make sure that citizens are secured and safe."
Foreign Minister Barnaba Marial Benjamin told the Associated Press that some soldiers had tried to raid the weapons store at the main military based in the capital, but were repulsed.
He said some politicians had since been arrested.
Mr Riek has not commented and his whereabouts are unclear. But his spokesman said he was safe and denied reports he had been arrested.
South Sudan - the world's youngest country and one of the least developed - has struggled to achieve a stable government since becoming independent from Sudan in 2011. The independence referendum was intended to end a decades-long conflict, led by the SPLM, against the north.
The oil-rich country is ethnically and politically divided, with many armed groups active. Tensions have been particularly high since President Kiir dismissed his entire cabinet, including Mr Machar, in July.
The sackings are believed to have followed a power struggle - Mr Machar has said he plans to contest the presidential elections in 2015. He now leads a dissident faction within the SPLM.
The two men are from rival ethnic groups that have clashed in the past. Mr Kiir is from the Dinka community, the largest in South Sudan, while Mr Machar is from the Nuer, the second-largest. Some Nuer have complained about Dinka political domination.
Juba was reportedly calm by mid-morning with few civilians on the streets, but heavily armed troops were seen patrolling.
Hundreds of people, mainly women and children, have taken shelter at the UN compound near the airport and at a UN house in the city.
A spokesman told Reuters seven people, including a two-year-old boy, had been treated for gunshot wound.
The UN said in a statement: "We hope the security situation in Juba will quickly normalise to enable the civilians to return very soon to their residential areas. To that end, UNMISS (the UN mission in South Sudan) calls on all parties to show continued calm and restraint."
The UN and the US embassy advised their citizens to stay at home. Both denied rumours they were harbouring any political or military figures.
Both Sudan and the South are reliant on their oil revenues, which account for 98% of South Sudan's budget. But the two countries cannot agree how to divide the oil wealth of the former united state. Some 75% of the oil lies in the South but all the pipelines run north. It is feared that disputes over oil could lead the two neighbours to return to war.
Although they were united for many years, the two Sudans were always very different. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.
The health inequalities in Sudan are illustrated by infant mortality rates. In South Sudan, one in 10 children die before their first birthday. Whereas in the more developed northern states, such as Gezira and White Nile, half of those children would be expected to survive.
The gulf in water resources between north and south is stark. In Khartoum, River Nile, and Gezira states, two-thirds of people have access to piped drinking water and pit latrines. In the south, boreholes and unprotected wells are the main drinking sources. More than 80% of southerners have no toilet facilities whatsoever.
Throughout the two Sudans, access to primary school education is strongly linked to household earnings. In the poorest parts of the south, less than 1% of children finish primary school. Whereas in the wealthier north, up to 50% of children complete primary level education.
Conflict and poverty are the main causes of food insecurity in both countries. In Sudan, many of the residents of war-affected Darfur and the border states of Blue Nile and South Kordofan, depend on food aid. The UN said about 2.8m people in South Sudan would require food aid in 2013. The northern states tend to be wealthier, more urbanised and less reliant on agriculture.