Even as the meeting took place, a spokesman for the South Sudanese military, Col. Philip Aguer, said that government forces were waging a pitched battle against rebels in Malakal, the capital of Upper Nile State, with the government controlling the city’s north and the rebels the south.

Image Credit... The New York Times

The crisis in South Sudan began last week after what Mr. Kiir described as a coup attempt by soldiers loyal to the former vice president, Riek Machar. Mr. Kiir dismissed Mr. Machar and the entire cabinet in July. Mr. Machar remains in an undisclosed location after fleeing the capital. Many of his allies were arrested, and he has said their release is a precondition for starting talks, a position Mr. Kiir has rejected.

But the political dispute has spiraled into a broader humanitarian crisis. The United Nations special representative to South Sudan, Hilde Johnson, said in a videoconference from the capital here on Thursday that well over 1,000 lives had already been lost in the conflict. More than 50,000 people are seeking refuge at United Nations compounds across the country. The peacekeeping force is overstretched trying to protect them, she said, adding that she expected reinforcements of personnel and equipment within 48 hours.

Ms. Johnson said the United Nations did not see the conflict coming. “We knew that there were tensions and that this could lead to problems, but I don’t think any South Sudanese, nor any of us observers, in country or outside, expected an unraveling of the stability so quickly,” she said.

The dispute stems from a power struggle between grudging collaborators turned outright rivals, but the violence quickly shifted into attacks against civilians and reprisals between ethnic groups. Mr. Kiir is a Dinka, the country’s largest ethnic group, while Mr. Machar is a Nuer, its second largest. South Sudan declared independence from Sudan in 2011 after decades of civil war.