In this photo released by the United Nations Mission in South Sudan (UNMISS), the remains of two Indian U.N. peacekeepers who were killed Thursday arrive back at the airport in Juba, South Sudan Friday, Dec. 20, 2013. The U.N. peacekeeping mission in South Sudan says two Indian peacekeepers were killed at their base when armed youths breached the U.N. compound in Akobo, Jonglei state, and called "on all parties to the crisis to refrain from further violence and seek a peaceful resolution." In this photo taken on Thursday, Dec. 19, 2013 and released by the United Nations Mission in South Sudan (UNMISS) on Friday, Dec. 20, 2013, UNMISS troops from Bangladesh assist civilians at the UNMISS compound in Juba, South Sudan. The U.N.'s humanitarian arm said Friday that 34,000 people in South Sudan are seeking refuge at U.N. bases in three locations across the country, following recent fighting. JUBA, South Sudan (AP) - Armed rebels were said to be in control of some of South Sudan's oil fields Friday, raising questions of how long the country's oil will flow and whether Sudan could enter the conflict. President Salva Kiir implored his country to turn away from ethnic violence and met Friday with foreign ministers from neighboring states, including Kenya and Ethiopia, who flew into Juba, the capital, to help calm tensions after a week of ethnic strife that is estimated to have killed hundreds. Kiir did not speak publicly, but the government's Twitter feed attributed this quote to him: "Those who may want to take the law into their hands, the long arm of the government will get them." The United Nations expressed alarm at an attack by "approximately 2,000 armed elements" on a U.N. base in Jonglei state that killed two peacekeepers from India. A statement from the secretary-general's office said a number of civilians seeking refuge there Thursday were killed. Fighting continued to spread on Friday in Jonglei and Unity state, an oil area, as armed groups opposed to the nation's military emerged, said a South Sudan expert communicating with combatants and U.N. officials in strife-torn regions outside the capital. We've seen the conflict expand quite rapidly and quite dramatically in recent days. We've seen the emergence of different armed groups under different commands, and we've seen the former vice president say he's not interested in talks that don't end in Salva Kiir stepping down," said Casie Copeland, South Sudan analyst for the International Crisis Group. She added that the arrival of regional foreign ministers in Juba "is genuinely a good thing." Armed opposition groups appeared to be in control of some oil fields in Unity state, she said. South Sudan's oil fields have historically been a target for rebel movements. "The potential for oil wealth to exacerbate the current power struggle should not be underestimated," said Emma Vickers of Global Witness, a London-based group that investigates and campaigns to prevent natural resource related conflict. If rebel forces were to capture the oil fields, they could effectively hold the government to ransom. The United Nations said Friday that 35,000 people continue to seek refuge at U.N. bases in three locations across the country, including 20,000 at two bases in the capital. The U.S. Embassy had a fifth emergency evacuation flight on Friday to move Americans out of the country. British, German and Dutch planes were also scheduled to fly out. Hundreds of foreigners, including aid workers, have hurriedly left South Sudan this week at the urging of foreign embassies concerned about the possibility of out-of-control violence. Forty-five U.S. troops were dispatched to Juba earlier this week to protect U.S. citizens and property. A top U.N. official in the country, Toby Lanzer, said Friday that "difficulties" continued in Jonglei state, including the province capital, Bor, where a top military commander loyal to Machar defected from the army this week, taking his troops with him. South Sudan gets nearly 99 percent of its government budget from oil revenues. The country reportedly earned $1.3 billion in oil sales in just five months this year, Global Witness said. South Sudan, the world's newest country, peacefully broke away from Sudan in 2011 after decades of war and years of negotiations that former U.S. President George W. Bush invested heavily in. The south's oil flows north through Sudan's pipelines, and a rebel takeover of southern oil fields could invite Sudan into the conflict. . Ethnic violence broke out among South Sudan's presidential guard late Sunday night, and fighting spread across the country over the next several days, leading to fears of a civil war between ethnic groups. Kiir, an ethnic Dinka, earlier this week said an attempted coup had triggered the violence, and the blame was placed on fired Vice President Riek Machar, an ethnic Nuer. But officials have since said a fight between Dinka and Nuer members of the presidential guard triggered the violence. Machar's ouster from the country's No. 2 political position earlier this year had stoked ethnic tensions. After meeting with Kiir, Ethiopia's Foreign Minister Tedros Adhanom Ghebreyesus said the ministers from a regional bloc known as IGAD were in the country to "understand the situation first hand." He called the meeting with Kiir productive but did not provide details. The U.N.'s humanitarian arm said 14,000 people are seeking shelter in Bor, the capital of Jonglei state, the scene of heavy violence this week. Several hundred people are also seeking shelter in Bentiu, the capital of Unity state. The U.N. sent four helicopters to Akobo, in Jonglei state, on Friday and said on Twitter that it "has received assurances from forces in charge" that the helicopters will be permitted to land. On Thursday armed youths breached the U.N. compound in Akobo, and two U.N. peacekeepers were killed. The U.N. mission also estimates that at least 11 of the civilians who sought refuge there were killed during the attack. Straziuso reported from Nairobi, Kenya. Rodney Muhumuza contributed from Kampala, Uganda. Associated Press writer Edith M. Lederer at the United Nations contributed.