Juba was rocked by several days of heavy fighting in early July
East African leaders will gather in Ethiopia on Friday to discuss a regional intervention force to back up UN troops in SouthSudan, an initiative vehemently opposed by President Salva Kiir.
Regional bloc IGAD has raised the possibility of deploying an "intervention brigade" with a more aggressive mandate within the UN mission currently present.
The 12,000-strong UN peacekeeping mission in South Sudan, UNMISS, has faced criticism for failing to stem the latest bloodshed or fully protect civilians during the fighting.
Juba was rocked by several days of heavy fighting in early July between the government forces of Kiir and those loyal to ex-rebel chief Riek Machar, the latest upsurge in two and half years of war.
Goi Jooyul Yol, a spokesman for Machar, told AFP in Addis Ababa "the only hope is a protection force. There is no security for the moment in Juba."
The mooted force for South Sudan would be modelled on the Force Intervention Brigade of 3,000 troops deployed within the UN's mission in the Democratic Republic of Congo, which proved decisive in neutralising the M23 rebellion in 2013.
Former vice-president Machar has refused to come back to Juba until the deployment of a neutral force of African troops -- a plan approved by the the US and African Union but rejected by Kiir.
"The peace agreement has collapsed. They have to find a way forward to restore calm in South Sudan," Jooyul added. Neither Kiir nor Machar is expected to attend the event.
Nearly 300 people have died in the violence so far, while 60,000 have fled the country.
On Wednesday, Kiir gave an interview to Kenya's KTN TV in which he once again dismissed the idea of the force.
"I don't see the reason why there should be a foreign intervention, to come and do what? there is no fighting in Juba," he said, comparing it to trespassing on his property.