The United Nations received reports from local sources in South Sudan on Tuesday that between 400 and 500 people had been killed and up to 800 wounded in the latest violence, and the government said it had arrested 10 politicians in connection with a "foiled coup".

"Two hospitals have recorded between 400 and 500 dead and (up to) 800 wounded," a diplomat in New York said on condition of anonymity, citing an estimate United Nations peacekeeping chief Herve Ladsous gave during a closed-door briefing for the 15-member body.

Another diplomat confirmed Ladsous' remarks, adding that the United Nations was not in a position to verify the figures.

Earlier on Tuesday, a South Sudanese health ministry official told Reuters that at least 26 people were dead after fighting in Juba between rival groups of soldiers from Sunday night into Monday morning. Sporadic gunfire and blasts continued up to Tuesday evening.

The Juba government said it had arrested 10 major political figures and was hunting for its former vice president, accusing him of leading a failed coup in the oil-producing country's capital, where gunfire rang out for a second day.

The prominence of the names, including former finance minister Kosti Manibe among those who had been detained, underlined the size of the rift in Africa's newest state, less than 2-1/2 years after it seceded from Sudan.

The United States urged its citizens to leave the country immediately, and said it was suspending normal operations at its embassy.

U.S. Secretary of State John Kerry, on a visit to the typhoon-ravaged central Philippine city of Tacloban, urged a "peaceful and democratic" solution.

"The United States believes very strongly that all parties should refrain from any action that could further escalate the tensions," Kerry told reporters. "Political differences need to be resolved by peaceful and democratic means, those that have been hard fought for."

The White House said President Barack Obama was getting briefings on the situation.

President Salva Kiir, dressed in military fatigues, said on television on Monday that forces loyal to former vice president Riek Machar, whom he sacked in July, had attacked an army base in a bid to seize power.

South Sudan is one of the poorest and least developed countries in Africa despite its oil reserves, and it is plagued by ethnic fighting.

The rift at the heart of its political elite will dismay oil companies that had been counting on a period of relative stability after South Sudan's independence so they could step up exploration. France's Total and some largely Asian groups, among them China's CNPC, have interests there.

It will also be closely watched by South Sudan's neighbors, which include some of the continent's most promising economies, including Ethiopia and Kenya.

After its meeting on the crisis in New York, the U.N. Security Council issued a statement saying it "urged all parties to immediately cease hostilities, exercise restraint and refrain from violence and other actions that could exacerbate tensions."

French U.N. Ambassador Gerard Araud, president of the council this month, told reporters the council would meet again in coming days on the upsurge in violence in South Sudan.

Kiir and Machar are from different ethnic groups that have clashed in the past. Machar leads a dissident faction inside the ruling Sudan People's Liberation Movement (SPLM) and was planning to run for the presidency.

Fighting erupted outside his compound in Juba on Tuesday, but his whereabouts were unknown, foreign affairs spokesman Mawien Makol Arik told Reuters. Machar has so far not released a statement.

The government on Tuesday accused him of being the "coup leader" and listed four other wanted men, including Pagan Amum, the SPLM's former Secretary General and the country's main negotiator in a prolonged oil dispute with Sudan.

"Those who are still at large will be apprehended," Information Minister Michael Makuei said in a statement on a government website. He said he believed they had fled to an area north of the capital.

The 10 officials had been arrested "in connection with the foiled coup attempt," the statement said.

Around 16,000 people had taken refuge in U.N. compounds in Juba by noon on Tuesday and the numbers were rising, the United Nations said.

Streets were empty at the start of a dawn-to-dusk curfew, ordered by the president. Mobile phone signals were down for a second day.-Reuters