Heavy fighting was raging Sunday in the South Sudanese capital Juba, with witnesses reporting gunfire, artillery and tanks on the streets following several days of clashes between government and rebel forces.
Officials at the president's office put the death toll at 270 people since Friday.
"There is a lot of shooting going on in the city," said Gregor Fischer, a German photographer. "We are hearing small gunfire and artillery." He also reported seeing government tanks and hearing helicopters.
Much of the fighting was reportedly taking place in the Jebel neighbourhood where Vice President Riek Machar – rebel leader until a unity government was formed in April – has his residence.
"There is heavy artillery in that direction," said an aid worker who did not want to be named.
Machar's spokesman Jamet Gatdet said President Salva Kiir's forces had attacked Machar's positions in Jebel and denied reports that rebel forces had fled to UN camps.
"They are in full control of all their areas around Jebel," Gatdet said on Facebook.
"Our forces have captured three tanks ... from President Kiir's forces who attacked Jebel site. They are repulsed. Their helicopter gunships have now stopped bombing Jebel after one of them was almost brought down," Gatdet said.
He also reported heavy fighting at Juba airport. Kenya Airways announced it had suspended flights to Juba "due to uncertain security situation."
"The city is in a kind of lockdown at the moment," Fischer said, adding it was not possible to pass through checkpoints.
The US embassy in Juba reported ongoing fighting "throughout Juba." The UN mission to South Sudan tweeted that there had been a "sustained clash" with heavy weapons close to its premises.
The violence has been going on since Thursday, when clashes erupted between government and rebel troops.
On Friday, fighting broke out near the presidential palace, where Kiir was meeting Machar.
Officials at the president's office put the death toll at 60 on Kiir's side and 210 on Machar's side. But hospital sources have also spoken of civilian casualties.
In December 2013, a power struggle between Kiir and Machar escalated into a military conflict that has killed tens of thousands and displaced more than 2 million people.
The formation of a unity government in April was expected to end the fighting, but the fresh outbreak of violence dealt a blow to such hopes, just as South Sudan marked the fifth anniversary of its independence from Sudan on Saturday.
The UN Security Council "strongly condemned" the fighting. The east African bloc Intergovernmental Authority on Development (IGAD), which mediated in the peace talks, said the violence had "once again placed the long suffering people of South Sudan in unspeakable harm's way."