UPDATE 2-Armed mob under guise of peaceful protest attacks UN in South Sudan
(Adds comment from U.S. State Department, paragraphs 9-13)
UNITED NATIONS, April 17 (Reuters) - A mob of armed civilians pretending to be peaceful protesters delivering a petition to the United Nations in South Sudan forced their way into a U.N. base sheltering some 5,000 civilians on Thursday and opened fire, the world body said.
A U.N. source, speaking on condition of anonymity, said at least 20 people had been killed and 60 wounded in the attack on the base in Bor in northern Jonglei state, where there are Indian and South Korean U.N. peacekeepers. The source warned that the death toll was likely to rise.
U.N. spokesman Stephane Dujarric said dozens of civilians were wounded, but the exact number of people killed or wounded had not yet been confirmed. Two U.N. peacekeepers were wounded repelling the armed mob, he said.
More than 1 million people have fled their homes since fighting erupted in the world's youngest country in December between troops backing President Salva Kiir and soldiers loyal to his sacked vice president, Riek Machar.
Thousands of people have been killed and tens of thousands have sought refuge at U.N. bases around the country.
"This attack on a location where civilians are being protected by the United Nations is a serious escalation," Dujarric said. "The assailants - a mob of armed civilians - came to the base under the guise of peaceful demonstrators intending to present a petition to UNMISS (the U.N. peacekeeping mission)."
"The armed mob forced entry on to the site and opened fire on the internally displaced persons sheltering inside the base," he said. "At the time of the attack there were some 5,000 displaced civilians ... inside the base."
Dujarric said the wounded were being treated at the U.N. compound.
The U.S. State Department condemned the attack.
"We reiterate our call upon the Government of South Sudan to end the violence and to fulfill its primary responsibility to maintain law and order and provide full support for the UNMISS mission to protect civilians," State Department spokeswoman Marie Harf said in a statement.
Her statement also condemned recent attacks and counter-attacks in the town of Bentiu by anti-government and pro-government forces in violation of a Jan. 23 Cessation of Hostilities agreement.
"The deliberate targeting of civilians during these attacks is unacceptable and those responsible for such acts must be held accountable," Harf said.
The statement called on both sides in the conflict to honor the Jan. 23 agreement and enter into an inclusive political dialogue.
South Sudanese rebels said on Tuesday they have seized Bentiu, the capital of oil-producing Unity state, and warned oil firms to pack up and leave within a week.
South Sudan seceded from Sudan in 2011 under an agreement to end decades of war.
The current conflict has disrupted oil production, which provides a hefty portion of the government's revenue. (Reporting and writing by Michelle Nichols; Additional reporting by David Brunnstrom in Washington; Editing by Leslie Adler, Andrew Hay and Cynthia Osterman)