South Sudan's warring leaders have signed a fresh ceasefire deal vowing to end more than eight months of conflict,andnbsp;according to mediators who threatened sanctions should the agreement fail once again.
East Africa's regional IGAD bloc, which mediated the talks between President Salva Kiir and his sacked deputy Riek Machar, called on the leaders to forge a unity government within 45 days.
Thousands of people have been killed and more than 1.8 million have fled civil war sparked by a power struggle between Kiir and Machar, who met on Monday for the first time in more than two months.
An IGAD communique welcomed the "signature by the warring parties" to the deal, "which obliges the parties to bring the conflict to an end".
Three previous ceasefire commitments have been broken within hours.
"As a region, we have to show any party which violates agreements that there are consequences to misbehaviour," Ethiopian Prime Minister Hailemariam Desalegn said at the summit of east African leaders, the AFP news agency reported.
"We are sending a clear message to the leaders of South Sudan. So delaying in the procedure will not be acceptable - if not the region will take action."
Kiir and Machar last met in June, when they agreed to form a unity government within 60 days. They missed that deadline amid continuing war.
Millions face famine
The United Nations has said the food crisis is the "worst in the world", and aid workers warn of the risk of famine if the conflict continues.
The warring parties have to understand that further delays in the peace process cannot be tolerated.
The IGAD communique expressed "serious concerns over the worsening humanitarian situation in South Sudan where millions face famine, and which presents a threat to the national security of the entire region".
Regional leaders at the summit included Djiboutian President Ismail Omar Guelleh, Kenya's Uhuru Kenyatta and Uganda's Yoweri Museveni.
Ugandan troops are supporting South Sudan's government forces in the battle against the rebels.
Fighting is between government troops, mutinous soldiers and militia forces divided by tribe.
"All agree that the peace process so far has been difficult, on a path wavering between hope and disappointment, between encouragement and scepticism," said UN envoy Haile Menkerios.
"The warring parties have to understand that further delays in the peace process cannot be tolerated."
UN Security Council envoys, who visited South Sudan's capital earlier this month, warned both the government and rebel leaders of "consequences" of continuing to fight.
Almost 100,000 civilians are sheltering in UN camps across South Sudan, having fled to the bases in December to escape killings and massacres, and who are now too fearful to return home.
Ceasefire monitor killed
On Saturday, an IGAD ceasefire monitor died after being arrested by rebels.andnbsp;Rebel forces arrested the IGAD monitor on Saturday after the team landed near the town of Bentiu, in war-torn northern Unity state, the bloc said.
It was not clear how the IGAD monitor, who was a member of South Sudan's army, died.
The UN said it was "reportedly due to natural causes", but IGAD vowed in a statement that "those responsible for the death will bear the consequences".
Rebel forces in Unity are led by Peter Gadet, who has been slapped with sanctions by both the United States and European Union for atrocities.
Other ceasefire monitors have been released, but the rebels continue to hold a UN helicopter, the UN peacekeeping mission said on Monday.