The UN Security Council has called on warring factions in South Sudan to immediately end the recent fighting and prevent the spread of violence.
In a unanimous statement, the council condemned the fighting "in the strongest terms" and expressed "particular shock and outrage" at attacks on UN sites.
It also called for additional peacekeepers to be sent to South Sudan.
More than 200 people are reported to have died in clashes since Friday.
The fighting broke out when troops loyal to President Salva Kiir and first Vice-President Riek Machar began shooting at each other in the streets of the South Sudanese capital, Juba.
Relations between the two men have been fractious since independence in 2011. Despite a peace deal last year ending a civil war, each side accuses the other of bad faith.
The weekend's violence later escalated, with tanks, helicopter gunships and troops using rocket-propelled grenades involved.
Those killed include a Chinese UN peacekeeper. Several other peacekeepers and a number of civilians are reported to have been injured in crossfire.
A UN spokeswoman in Juba, Shantal Persaud, said the latest fighting had caused hundreds of internally displaced people to take refuge in UN premises.
She said both South Sudanese leaders were responsible for implementing last year's peace agreement, which included a permanent ceasefire and the deployment of forces away from Juba.
Information Minister Michael Makuei told the BBC that the situation in the city was now "under full control" and civilians who had fled should return to their homes.
Mr Machar's military spokesman, Col William Gatjiath, accused officials loyal to the president of lying, and said there had been at least 10 hours of clashes on Sunday.
"The situation in South Sudan is uncontrollable because Salva Kiir and his followers are not ready to follow the peace agreement," he said.
In a statement on Sunday, the US state department said it strongly condemned the latest outbreak of fighting in Juba.
Spokesman John Kirby said Washington had ordered the departure of non-emergency personnel from the US embassy in Juba.
Mr Kiir and Mr Machar had met at the presidential palace on Friday and issued a call for calm.
Calm was apparently restored on Saturday but heavy gunfire broke out again on Sunday near a military barracks occupied by troops loyal to Mr Machar.
A US academic who studies Sudan, Eric Reeves, told the BBC Mr Machar was trying to orchestrate a coup against his rival, with the backing of President Omar Bashir of Sudan.
"This has been planned," he said. "That violence now seems to be part of a co-ordinated coup led by Riek Machar. This changes entirely the complexion of the crisis."