Kenyan President Uhuru Kenyatta says there is a "very small window of opportunity to secure peace" in South Sudan, where inter-ethnic fighting has left more than 1,000 people dead.
He commented on Friday as regional African leaders met in Nairobi to discuss South Sudan's spiraling unrest.
Mr. Kenyatta outlined a series of proposals at the IGAD summit, including the appointment of two "experienced" envoys for South Sudan.
He also urged the African Union, United Nations and "broader international community" to pledge more support to the troubled nation.
He said the IGAD would not accept the "unconstitutional overthrow" of South Sudan's democratically elected government.
Fighting broke out in South Sudan earlier this month, after President Salva Kiir accused his ex-deputy Riek Machar of attempting a coup.
Machar says the violence was the result of a purge of Mr. Kiir's political rivals.
The violence quickly took on an ethnic dimension, with members of President Kiir's Dinka ethnic group fighting against the Nuer group to which Machar belongs.
On Thursday, Mr. Kenyatta and Ethiopian Prime Minister Hailemariam Desalegn discussed South Sudan's unrest with Mr. Kiir, during a meeting in the South Sudan capital, Juba.
Ethiopian officials reported "good progress" following the emergency mediation talks.
But the fighting continued, with government forces battling rebels for control of the Upper Nile town of Malakal.
On Thursday, the U.N. said it hoped to put peacekeeping reinforcements in South Sudan within 48 hours.
U.N. envoy Hilde Johnson stressed the need for "unprecedented speed" to boost the U.N. presence. She said more than 50,000 civilians had sought refuge at U.N. bases in the country since the fighting erupted.
Johnson also urged the country's political leaders to rein in their forces and work for peace.
"It is absolutely fundamental that the leaders of the country and all political forces and communities now put their own identity as South Sudanese first and not their own identity as members of a particular community. It is on that account that this country can move forward out of a situation of violence and strife and onto a peaceful track."
President Kiis and Machar have said they are ready for dialogue, but the government rejected Machar's demand that detained opposition leaders be released first.