South Sudan's President Salva Kiir says an attempted coup by soldiers loyal to his sacked former deputy Riek Machar has been put down.

This is said to have come after heavy gunfire overnight in the capital, Juba.

Mr. Kiir told reporters in the capital that the government was in full control and the culprits being pursued, and announced a night-time curfew.

Several people are reported wounded and hundreds of civilians have sought refuge at the UN mission in Juba.

The UN has expressed concern and appealed for calm. It said it was in touch with the government.

Hilde Johnson, the 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.