The United Nations' humanitarian coordinator in South Sudan said Tuesday that he had "absolutely no doubt" that thousands of people had been killed in violence that threatens to tear the world's newest country apart a little more than two years after it won independence.
Toby Lanzer made the remarks quoted by Sky News after U.N. investigators discovered two mass grave in the rebel-held city Bentiu in the oil-rich Unity state. Human rights office spokeswoman Ravina Shamdasani told the Associated Press that one grave contained 14 bodies and a site nearby contained 20 bodies. Originally the U.N. said 75 bodies had been seen but later corrected that statement to 34 bodies seen and 75 people missing and feared dead.
In New York, the U.N. Security Council voted unanimously to beef up its peacekeeping force in South Sudan. It condemned targeted violence against civilians and ethnic communities and called for "an immediate cessation of hostilities and the immediate opening of a dialogue."
A U.S. military spokesman said Tuesday that a platoon of Marines and an aircraft had been moved from Camp Lemmonnier in Djibouti to the Entebbe airfield in Uganda in order to respond more quickly if they are asked to evacuate any Americans remaining in South Sudan.
The government, meanwhile, announced that its military forces had taken back another key city, Bor, from the rebels who held it over the last week.
The government minister of information, Michael Makuei Lueth, said Bentiu is under the control of rebels loyal to the country's former vice president, Riek Machar, indicating they were responsible for the killings.
The dead in Bentiu reportedly were ethnic Dinka who belonged to the Sudan People's Liberation Army, said Shamdasani, referring to government military forces.
South Sudan President Salva Kiir is Dinka, the country's largest ethnic group, while Machar is Nuer, the second-largest ethnic group.
U.S. Secretary of State John Kerry spoke on the phone Tuesday with Machar, who said he told Kerry he is ready for talks with Kiir, likely to take place in Ethiopia.
"The United States urges all parties in the crisis in South Sudan to implement an immediate cessation of hostilities," State Department spokesperson Jen Psaki said in a statement released on Tuesday. "This will offer critical humanitarian access to populations in dire need and open a space for a mediated political dialogue between the opposing sides."
"The ability of the parties to implement the ceasefire will send a strong signal to the citizens of South Sudan and the world that as leaders they have the courage to accept compromise and work for the best interests of all of the people of this young nation," she added.
Machar said, also on Tuesday, to Radio France Internationale; "I will form a high-level delegation, to which I will give full power to negotiate an accord. We want Salva Kiir to quit power. We want a democratic nation and free and fair elections."
U.N. Secretary-General Ban Ki-moon, reiterating his call for Kiir and opposition leaders to end the crisis, said: "Whatever the differences, nothing can justify the violence that has engulfed their young nation."
"There is no military solution to this crisis," Ban stressed. "This is a political crisis which requires a peaceful political solution."
Violence began spreading across South Sudan after a fight among Kiir's presidential guards late Dec. 15, pitting Nuer against Dinka.
Some 20,000 people seeking safety have crowded round the U.N. base in Juba, the capital, where at least two other mass graves are reported to have been found, U.N. human rights chief Navi Pillay said.
The U.N. humanitarian office said 45,000 people have taken refuge in and around U.N. bases in the country, and 81,000 people have fled their homes as a result of the fighting.
However, a U.N. report quoted by Sky News said "Given the limited access to civilians outside population centres, the number is likely to be significantly higher."
The Security Council voted to temporarily increase the number of U.N. military personnel in South Sudan from 7,000 to 12,500, and the U.N.'s international police contingent from 900 to 1,323.
To reach the new levels, the resolution authorizes the temporary transfer of troops, police and equipment from the U.N. missions in Congo, Darfur, Abyei, Ivory Coast and Liberia.
Ban recommended in a letter to the council on Monday that the peacekeeping mission be beefed up and asked for three attack helicopters, three utility helicopters, and a C-130 military transport plane as well as other critical equipment.
After the vote, the secretary-general cautioned that strengthening the U.N. mission "will not happen overnight" — and even with additional manpower and equipment "we will not be able to protect every civilian in need in South Sudan."
"The parties are responsible to end the conflict," Ban stressed.
The United States, Norway and Ethiopia are leading efforts to open peace talks on the 10-day-old crisis. Officials say Kiir and Machar have agreed to meet but specifics, including the status of Machar's imprisoned compatriots, are holding up talks.
South Sudan's U.N. Ambassador Francis Deng assured the Security Council after the vote that the government "is doing as much as it can, under very difficult circumstances, to restore calm and stability to the affected areas in the country."
"South Sudanese do not want to fall back into the abyss of war from which they have suffered for over half a century," he said.
Deng repeated a statement from Kiir on Tuesday calling for an end to violence and ethnic targeting, and calling on Machar and the forces supporting him "to rise to the challenge of peace, unity and nation building."
South Sudanese troops, meanwhile, advanced on Bor on Tuesday, said military spokesman Col. Philip Aguer. The government said on Twitter later that it was clearing out remaining rebel forces.
The U.N. has staff in the country investigating mass killings, said Pillay, the U.N. rights chief. It is unclear who is responsible for the deaths, she said. Two other mass graves were reportedly found in Jebel-Kujur and Newside, near Eden, she said.
The country's top U.N. humanitarian official, Toby Lanzer, said Monday that he believes the death toll from 10 days of violence has surpassed 1,000 but added that there are no firm counts.
A top European Union official, Catherine Ashton, said political dialogue must include all groups, including those whose leaders are currently imprisoned. The use of force, she said, will achieve nothing.
"I am extremely concerned that South Sudan risks spiraling into a disaster for both its own people and the region. Such a situation can, and must, be avoided," Ashton said.
Hilde F. Johnson, head of the U.N. Mission in South Sudan, called the scale of the crisis "unprecedented" for the mission, and urged more resources to help people in U.N. camps across the country.
She also called on all those in South Sudan to refrain from "any community motivated violence."
The Security Council condemned "reported human rights violations by all parties, including armed groups and national security forces" and called for those responsible to be held accountable.
South Sudan, the world's newest country, peacefully broke away from Sudan in 2011 following a 2005 peace deal. Before that, the south fought decades of war with Sudan. The country, one of the world's least developed, still has pockets of rebel resistance and sees cyclical, tribal clashes that result in hundreds of deaths.
The Associated Press contributed to this report.