South Sudanese President Salva Kiir on Monday declared a unilateral ceasefire with immediate effect following several days of fighting with troops loyal to former rebel leader Riek Machar.
His spokesman, Ateny Wek Ateny, said the president had talked to Machar, who was sworn in as his deputy in April.
The two talked through a third party and "agreed that if the president should declare a ceasefire, Machar will do the same," Ateny said.
Local radio station Eye Radio reported that Machar had also ordered an immediate ceasefire.
Fighting meanwhile subsided in the capital Juba, although witnesses said some gunfire could still be heard.
The presidency had on Sunday put the death toll at 270 since Friday, but the figure was now believed to be higher.
UN Secretary General Ban Ki-moon called on the Security Council to implement an arms embargo immediately against South Sudan and to bolster a UN peace mission in the country.
Ban also called for sanctions against all parties that have hindered the implementation of a peace accord signed in August 2015.
The UN mission to South Sudan said two peacekeepers were killed and several injured in the latest violence. Chinese state broadcaster CCTV tweeted the two fatalities were Chinese. The UN Security Council said Chinese and Rwandan peacekeepers had been "killed or injured."
The UN mission said the use of heavy weapons had killed eight and injured 59 people in or near its camps for displaced people.
The fighting had intensified earlier Monday, with residents reporting the use of heavy artillery. Local broadcaster Radio Tamazuj reported large explosions in several neighbourhoods.
In the Ethiopian capital, Addis Ababa, a spokesman for Machar said several of his bodyguards and family members had been killed in attacks by the army in the Juba neighbourhood where the vice president resides.
Kenya Airways and Rwandair cancelled flights to Juba. The US State Department and a peace process monitoring commission set up by the regional bloc, Intergovernmental Authority on Development (IGAD), said their staff was leaving the country.
The fighting was meanwhile reported to be spreading to other towns, including Torit in the south.
"Our reporter in Torit says hundreds of people running to the UN compound following a shoot-out this morning," UN-operated Radio Miraya tweeted. City officials later said an attack by unknown gunmen had been repelled, a local journalist told dpa.
The UN mission said more than 7,000 people had fled fighting to its compounds.
UNHCR was preparing for an influx of thousands of South Sudanese refugees into Uganda, but South Sudan had closed border crossings and many refugees were stranded on the border, said Charles Yaxley, spokesman for the UN Refugee Agency.
"Two-thirds of those displaced are children and so nutrition requirements need to be stockpiled. The refugees are robbed of all their possessions by members of armed groups," Yaxley said.
Uganda was allowing people to come in from South Sudan, Ugandan police spokesman Fred Enanga said, while not allowing anyone to cross over into South Sudan for security reasons.
Enanga said two Ugandans working in Juba had been shot dead and that Uganda had evacuated more than 300 of its citizens by bus.
Clashes erupted between army and the rebels on Thursday, followed by fighting on Friday near the presidential palace.
The fresh outbreak of violence dealt a blow to hopes of peace after Kiir and Machar signed the peace agreement last year and formed a national unity government in April.
A power struggle between the two escalated into an armed conflict in December 2013, killing tens of thousands and displacing more than 2 million people.
"Juba has been a tinderbox since April 2016 when soldiers from both sides were cantoned in the city’s environs," said Emma Gordon, senior East Africa analyst at risk consultancy Verisk Maplecroft.
"A return to fighting in the capital was inevitable due to the failure to demilitarize the area and a total lack of trust between the two sides," she added.
"Continuation of the civil war is all but inevitable," Gordon said.