Kampala -- A US plane was hit by gunfire Saturday as it was evacuating people from South Sudan, said a military official in Uganda, where the plane made an emergency landing.
"It was the US plane that was hit, and it landed in northern Uganda," military spokesman Paddy Ankunda said.
CNN quoted Pentagon spokesman John Kirby as saying four US service members were injured when gunfire hit their aircraft as it was trying to land in Bor, the capital of South Sudan's Jonglei state, an epicentre of violence in the past week.
The United States is one of several nations, including Uganda, that are evacuating citizens from the chaos emerging in South Sudan, where some military units are revolting against the central government.
Kenyan President Uhuru Kenyatta has ordered the deployment of troops to South Sudan to evacuate 1,600 Kenyan citizens, most of whom are based in Jonglei, where the hostilities are strongest.
According to the United Nations, more than 35,000 people - including citizens from the US, South Africa, Australia, Canada and Kenya - are sheltering in the organization's compounds in Juba and Bor.
"We've heard clashes and seen bodies in the streets," Toby Lanzer, the UN humanitarian coordinator in South Sudan, said on his Twitter feed after visiting conflict areas in Bor. "Civilians have left town to flee for their safety."
African nations are working to negotiate a ceasefire in the world's newest nation, but there was no indication the talks were leading to any political deals.
US Secretary of State John Kerry said he was also sending a special envoy to help with the talks.
The violence in South Sudan, which became independent in 2011, began Sunday when troops apparently loyal to former vice president Riek Machar launched attacks on army bases.
Machar, who was sacked this year, has said he wants President Salva Kiir to step down.
"The talks have been hampered by the refusal by Machar to talk with Kiir as president," said an African official with close knowledge of the negotiations. "He wants Kiir to resign first."
Hundreds of people have died this week in the fighting - which some analysts and government officials have described as an attempted coup - including two UN peacekeepers from India.
Nkosazana Dlamini-Zuma, the African Union chief, said the killings of the peacekeepers was a "war crime." She also urged the South Sudanese leadership to "halt the slide towards civil war."
Dlamini-Zuma said she "is profoundly dismayed at the recent turn of events that puts at risk countless human lives and jeopardizes the fundamental viability of the South Sudanese nation."
The conflict has ethnic overtones, sparking concerns that the escalation of the conflict could take on tribal dimensions. There have already been reports of harassment by soldiers and police based on ethnicity.
Kiir is a Dinka, South Sudan's largest ethnic group, while Machar is Nuer.
During the decades of conflict with Sudan, many of the South's ethnic clashes were brushed aside in favour of a focus of fighting Khartoum. However, since its independence, ethnic rivalries have become a major problem in South Sudan.
In Jonglei alone, more than 1,000 people have been killed in recent years in tit-for-tat cattle raids between Dinka and Nuer tribes.