South Sudan Says Coup Defeated after Heavy Fighting

South Sudan's president announced Monday he had defeated a coup attempt following a night of fierce fighting between rival troops in the capital of the world's youngest nation.

The clashes broke out in a barracks close to the city center shortly before midnight and spread across the city, diplomats and witnesses said, adding that heavy machine guns and mortars were used.

The United Nations said hundreds of terrified civilians had sought refuge in a U.N. compound, while across the city residents locked themselves in their homes or tried to flee to safer areas, an AFP reporter said.

President Salva Kiir blamed troops loyal to his arch-rival, former vice president Riek Machar who was sacked from the government in July. He branded him a "prophet of doom" and vowed to bring him to justice.

"Your government is in full control of the security situation in Juba. The attackers fled and your forces are pursuing them. I promise you justice will prevail," the president said in a televised address to the nation.

He said an overnight curfew would be imposed from 6:00pm to 6:00am (1500 to 0300 GMT), and would remain in force until further notice. A diplomat in the city said troops loyal to the president had been posted at major intersections, while civil aviation sources said that Juba airport had been shut.

"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," said Kiir, who was dressed in military uniform rather than his trademark suit and cowboy hat.

Army spokesman Phil Aguer also told local radio that troops loyal to the president were "in control of the situation".

Officials said some arrests had been made, and there were unconfirmed reports of several former ministers being detained. But the fate of Machar was unclear -- with the U.S. embassy in Juba and the U.N. dismissing speculation they had given him shelter.

There was also no word on casualties from the fighting.

Machar leads a dissident group within South Sudan's ruling party -- the Sudan People's Liberation Movement (SPLM) -- and is seen as the main challenger to Kiir. The rivals hail from different ethnic groups and had in the past fought on different sides during Sudan's civil war.

Oil-rich but impoverished South Sudan won its independence in 2011 after its people voted overwhelmingly in a referendum to split from the north and form a new nation.

But the country has struggled with ethnic violence and corruption, and political tensions have worsened in recent weeks.

Earlier this month key SPLM leaders -- including Machar and Rebecca Garang, the widow of South Sudan's founding father John Garang -- made a public challenge to Kiir, accusing him of being "dictatorial".

Statements from the U.S. and British embassies in Juba urged their nationals to avoid unnecessary movements. The U.S. embassy said there had been "incidents and sporadic gunfire in multiple locations across Juba" throughout the night.

The United Nations said it was "deeply concerned" over the fighting and that it was in contact with South Sudan's leadership.

"As the special representative of the secretary general, I urge all parties in the fighting to cease hostilities immediately and exercise restraint," U.N. Special Representative Hilde Johnson said in a statement.

"I have been in touch regularly with the key leaders, including at the highest levels, to call for calm," she added.

A spokesman for the U.N. mission in South Sudan, UNMISS, said hundreds of civilians had sought shelter at a U.N. compound.

"We have more than 800 civilians who came into our compound adjacent to the airport, mostly women and children. Among them are seven wounded, including a two-year-old boy in a critical condition," Joseph Contreras told AFP.

"While UNMISS is not a humanitarian operator, and our mandate is to protect civilians, basic water supplies and medical treatment are being provided. We hope the security situation in Juba will quickly normalize to enable the civilians to return very soon to their residential areas," UNMISS also said in a statement.