Deadly clashes between rival army factions are spreading in South Sudan, with at least 19 civilians killed in one high-risk town, the United Nations said Wednesday.
Hundreds are already feared killed in the capital Juba in fighting pitting troops loyal to President Salva Kiir against soldiers who support his former vice president Riek Machar.
South Sudan's Red Cross reported at least 19 civilians killed Wednesday in new battles in Bor, capital of Jonglei state, UN spokesman Martin Nesirky told reporters.
The deaths were reported after clashes between factions of the Sudan People's Liberation Army (SPLA) at a military camp in Bor, Nesirky said.
He added that "tensions seem to be on the rise in Unity and Upper Nile states."
UN officials in South Sudan have also reported fighting in the Equatorial State capital of Torit.
Kiir is an ethnic Dinka while Machar is from the rival Nuer group, and UN officials and diplomats have raised concerns that the battle between them could become a wider ethnic conflict.
Jonglei has long been a center of the ethnic tensions between the rival groups. Thousands have been killed in unrest in Jonglei since South Sudan, the world's newest state, became independent in 2011.
Nesirky said 800 people have sought refuge at a UN compound in Bor.
Almost 20,000 are crowded into two UN missions in Juba where there are concerns over water supplies and sanitation.
Nesirky added however that Juba "appears to have calmed down to some degree except for reports of gunfire in parts of the city overnight."
UN leader Ban Ki-moon said the UN mission in the strife-torn country is still verifying reports that up to 500 people had been killed in Juba since the army factions started fighting on Sunday.
Kiir has accused Machar of attempting a coup, but the former vice president has denied this and UN officials and diplomats say it is not yet clear what led to the unrest.
"This is a political crisis, and urgently needs to be dealt with through political dialogue," Ban told reporters as he welcomed reports that Kiir has offered talks to his opponent.
But the UN secretary general added: "It is essential to protect the human rights of all those who are detained. Mandated human rights monitors must have full access to visit the detainees. Security forces must operate in full compliance with international humanitarian law."
Kiir's government has said that a number of arrests, including of former ministers, have been made since Sunday.
The United Nations has a major peacekeeping operation in South Sudan, which became independent after an acrimonious split with Sudan.
The United Nations is not yet considering withdrawing staff from the country, Nesirky said.