The United Nations is sending 5,500 additional peacekeepers to South Sudan, where a U.N. official reported thousands of people have likely been killed since fighting began there last week.
The U.N. Security Council approved a measure Tuesday to boost its overall force to nearly 14,000 peacekeepers. U.N. chief Ban Ki-moon said "it may take time" for the troops and police to deploy, and reiterated his call for the country's leaders to resolve their differences through dialogue.
U.S. Secretary of State John Kerry called both President Salva Kiir and former vice president Riek Machar on Tuesday, urging them to halt the fighting and hold mediated political talks.
Both men have said they are ready for dialogue, but the government rejected Machar's demand that detained opposition leaders be released first.
The government said that forces loyal to Machar remain in control of Bentiu, one of two state capitals seized by renegade soldiers last week. It said on Tuesday that the army retook the other city, Bor, and was clearing out remaining rebel forces.
The same day, the U.N. human rights office said a mass grave was discovered in Bentiu, the capital of Unity State. Spokeswoman Ravina Shamdasani told VOA that a U.N. official saw 14 bodies in a grave and 20 at a nearby riverside.
She indicated the bodies could be those of some 75 Dinka army soldiers unaccounted for and feared dead.
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Kiir, an ethnic Dinka, has blamed Machar, an ethnic Nuer, of masterminding an alleged coup attempt December 15.
The United States says 150 Marines have been moved to Djibouti, ready to enter South Sudan to evacuate Americans and protect U.S. facilities.
The White House on Tuesday released Dinka- and Nuer-language versions of a recent statement by President Barack Obama, appealing for an end to the violence.