By Marie-Louise Gumuchian
Up to 40,000 civilians have taken refuge in United Nations bases in South Sudan, the organization said Sunday, as they seek shelter from a spiraling conflict in the world's newest nation.
After a deadly attack on one of its compounds where civilians had fled to, the United Nations is boosting its mission on the ground, Secretary-General Ban Ki-moon said.
"These 40,000 civilians who took refuge in the United Nations compound -- they are very much vulnerable," Ban told a news conference in the Philippines.
"There are many more thousands of people who are very much in fear and vulnerable, and at this time, the priority of the United Nations is to (protect) the lives of civilians."
Hundreds of people have been killed in a week of fighting, which has spread from the capital Juba to oil fields farther north.
South Sudanese President Salva Kiir blamed soldiers loyal to his former Vice President, Riek Machar, for starting the violence.
As the fighting spreads, foreign countries have been airlifting their citizens out.
On Saturday, the U.S. aborted a mission to evacuate Americans when its aircraft carrying military members was fired upon as it prepared to land in the town of Bor, wounding four of them, the Pentagon said.
The most severely damaged aircraft was thought to have been hit in the fuel line, a military official said speaking on condition of anonymity.
All three aircraft -- CV-22 Ospreys -- were diverted to Entebbe, Uganda, the official said. Another aircraft then flew the wounded to Nairobi, Kenya, U.S. Africa Command said in a statement. The four service members were in stable condition after treatment.
Tensions have been high in South Sudan since July, when Kiir dismissed Machar and the rest of the Cabinet. The move inflamed tensions between Kiir's Dinka community and Machar's Nuer community.
The United Nations said some 20 people were killed during an attack by about 2,000 armed youths on a U.N. peacekeeping base in Jonglei state. Two Indian peacekeepers were also killed.
After the deadly attack, the assailants fled with arms, ammunition and other supplies, the U.N. said.
"We also seeking support from other key countries who can provide the necessary assets," Ban said. We are in shortage of capacity. When the United Nations compound was overrun by 2,000 armed elements, we were having difficulties. "
Echoing calls from Western governments, Ban urged an end to the violence and called on Kiir and Machar "to come to the table and find a political way out of this crisis".
"They are responsible to the people of South Sudan to end the crisis and find the political means of addressing their differences," he said.
Ban said he had dispatched a special representative to Juba to work with the U.N. envoy in the city. The United States is also sending an envoy.
South Sudan formally split from Sudan in 2011 after a referendum, following decades of conflict. Numerous armed groups remain active in the oil-rich country.
CNN's Anna Maja Rappard, Barbara Starr and Tom Watlkins contributed to this report
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