- A diplomat in the city described the situation as "quite confused"
- A security source said the fighting broke out shortly before midnight Sunday
The United Nations said Monday it was "deeply concerned" over fighting in South Sudan's capital Juba and that it was in contact with the nation's leaders to call for calm.
"As the Special Representative of the Secretary General I urge 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," the Special Representative of the Secretary-General, Hilde Johnson, said in a statement.
Heavy gunfire erupted overnight, diplomats said, amid mounting political tensions in the newly-independent nation.
Diplomats and security sources said the fighting appeared to have broken out in a barracks close to the city centre shortly before midnight and involved the use of heavy machine guns and mortars.
Political tensions have been high in South Sudan in recent weeks, and earlier this month key leaders of the ruling party - the Sudan People's Liberation Movement (SPLM) - made a public challenge to President Salva Kiir and accused him of "dictatorial" behaviour. (READ: Kiir names new ministers, governor)
South Sudan's Information Minister Michael Makuei Lueth refused to comment on the unrest, but signalled the president was still in charge.
"The president is going to speak soon. I can't say anything until he speaks," he said.
A diplomat in the city described the situation as "quite confused", but added that relative calm returned to the city at 9:00 am with troops posted at major intersections.