U.N. Secretary-General Ban Ki-moon is calling for calm in South Sudan's capital, where the government says it is fighting off a coup attempt.
U.N. spokesman Martin Nesirky says Mr. Ban spoke by phone Tuesday with South Sudan's President Salva Kiir and expressed concern about the fighting and reports that, in his words, certain communities are being targeted.
"The secretary-general urged all parties to cease hostilities immediately, and called on the government to exercise restraint in the management of the situation and to guarantee the protection of all civilians regardless of their ethnicities."
On Monday, President Kiir said forces loyal to his former vice president, Riek Machar, attacked an army headquarters as part of an attempted coup.
Mr. Kiir fired Machar in July. Observers have expressed concern that the rift between Machar, from the Nuer ethnic group, and Mr. Kiir, a Dinka, could fuel tribal violence in South Sudan.
More gunfire was heard in Juba Tuesday, a day after Mr. Kiir insisted his forces had "full control" of the security situation in the city.
Government officials say the violence has killed at least 26 people, while a U.N. radio station reported that doctors at a local hospital have treated more than 100 people for gunshot wounds.
U.N. diplomats said Tuesday they were told that local sources in Juba put the death toll at 400 to 500, but that figure could not be verified.
The president of the U.N. Security Council, French Ambassador Gerard Araud, said as many as 20,000 people have taken refuge with the U.N. mission in Juba.
The U.S. State Department has ordered the departure of all non-essential personnel from South Sudan and is urging all Americans in the country to leave immediately.
In a Tuesday briefing, State Department spokeswoman Marie Harf said the U.S. is "deeply troubled" by the continued fighting and is urging South Sudan's political leaders to refrain from any action that could further escalate tensions.
South Sudan's government said 10 people have been arrested for their alleged roles in the coup attempt, while Machar remains at large.
Government security forces have imposed a nighttime curfew in Juba and were searching door-to-door for those blamed for the fighting.
The United Nations Mission in South Sudan estimates that 10,000 civilians have sought protection at two of its compounds in Juba, with 39 people receiving medical treatment.
Hilde Johnson, the U.N. special representative for South Sudan, has urged South Sudan's leaders to "refrain from any action that fuels ethnic tensions" and makes the violence worse.