Julio Brathwaite/UNMISS/AFP
UN peacekeeping chief Herve Ladsous added that another 800 people have been wounded in battles between troops loyal to President Salva Kiir and an opposition leader, according to diplomats in the closed council consultations on the new crisis in Africa.
Ladsous said the information was based on reports given by Juba hospitals but the UN has not yet confirmed the toll amid new clashes on Tuesday.
About 15,000 people have sought refuge in UN compounds around Juba since the troubles started on Sunday, the official was quoted as saying.
Juba remains "extremely tense" and it appeared the clashes were being carried out between ethnic groups, Ladsous told the 15-member council.
Salva Kiir has accused troops loyal to former vice president Riek Machar of staging a coup attempt in the impoverished nation. The government said 10 key figures including ex-ministers have been arrested, but that Riek Machar was on the run.
Salva Kiir is an ethnic Dinka while Riek Machar is a Nuer.
UN leader Ban Ki-moon spoke with Salva Kiir on Tuesday and urged him to offer "dialogue" with the opposition. Ban also spoke with the president of neighboring Uganda, Yoweri Musseveni, about the unrest, officials said.