A group of East African foreign Ministers will travel to South Sudan on Thursday to seek an end to days of fighting, the first foreign mission to enter the country since the eruption of the conflict that has killed up to 500 people.

Clashes between rival groups of soldiers started in the capital Juba late on Sunday and spread on Wednesday to the flashpoint town of Bor, scene of an ethnic massacre in 1991, raising fears of a slide into civil war.

South Sudan's President Salva Kiir has accused his sacked deputy Riek Machar of starting the fighting and trying to launch a coup, charges denied by Machar. Kiir said on Wednesday he was ready for dialogue.

"We will travel to Juba tomorrow to gain first-hand knowledge of the situation on the ground, and discuss ways to seek a political settlement to the crisis," Ethiopian Foreign Affairs Minister Tedros Adhanom told Reuters.

"This is our neighbourhood and we are hopeful that this situation will be solved amicably."

The ministers will travel under the umbrella of the East African trade bloc the Intergovernmental Authority on Development.