South Sudanese President Salva Kiir on Wednesday called for an end to ethnically based attacks on civilians, even as fighting raged in a key oil-producing region and a fast-spreading humanitarian crisis worsened.

“Whoever is still doing whatever malicious things in the residential areas, they must be told to stop,” Kiir told congregants at Christmas Mass in Juba’s largest cathedral, St. Theresa’s. “That is not supporting me. Instead you are destroying me.”

Kiir’s appeal comes amid widespread reports of extrajudicial killings, rapes, beatings and mass graves, according to victims, witnesses and U.N. human rights officials, raising fears of a civil war.

Ethnic Dinka government soldiers are accused of killing ethnic Nuer civilians in Juba, the capital, while Nuer gangs have targeted Dinka civilians in the towns of Bor, Bentiu and elsewhere in this fragile oil-producing nation, which gained independence from Sudan in 2011.

Kiir, dressed in light-blue traditional attire without his trademark black cowboy hat, first addressed the crowd in English. Switching to Arabic, he later said: “This is our third Christmas in an independent state, and they ruined this Christmas for us. We are not happy because some people are not here. Because they lost loved ones. . . . Tribal fighting will lead us nowhere.”

Even as Kiir spoke, government soldiers were fighting troops loyal to former vice president Riek Machar in Malakal, the capital of the oil-rich state of Upper Nile, said South Sudanese military officials. The clashes have continued despite efforts by the United States, as well as European and African nations, to mediate an end to the violence.

The crisis erupted Dec. 15 when soldiers loyal to Machar, who is a Nuer, clashed with troops loyal to Kiir, who is a Dinka, in Juba. That prompted Kiir to accuse Machar of attempting a coup. Since then, the violence has quickly spread to half of South Sudan’s 10 states.

On Wednesday, the United Nations announced that the number of people who have sought shelter at U.N. peacekeeping bases nationwide had mushroomed to 58,000. More than 92,000 have fled their homes.

In Malakal, 40 people have been treated for bullet wounds at the main hospital, including five who subsequently died, said Michael White, head of mission for Doctors Without Borders in the country. The casualty toll is expected to rise. The fighting in the town on Wednesday was more intense, and sounds of tanks and rocket-
propelled grenades reverberated through the streets, White said.

In a tweet Wednesday, Toby Lanzer, the deputy special representative to the U.N. mission in South Sudan, wrote that aid organizations need $166 million immediately “to provide the best protection and aid to civilians struck by evolving crisis.”