JUBA (AFP) - Thousands of South Sudanese have been killed in over a week of violence with reports of bodies piled in mass graves, the United Nations (UN) said on Tuesday, as the Security Council agreed to nearly double its peacekeepers in the young nation threatening to slide into civil war.
The top UN humanitarian chief in the country Toby Lanzer said Tuesday there was "absolutely no doubt in my mind that we're into the thousands" of dead, the first clear indication of the scale of the conflict engulfing South Sudan, which won independence from Sudan to much fanfare just two years ago.
However, the government also celebrated on Tuesday the important and strategic recapture of the key town of Bor after a nearly week-long rebel occupation, although large areas of the country remain out of their control.
Earlier, UN rights chief Navi Pillay said a mass grave had been found in the rebel-held town of Bentiu, while there were "reportedly at least two other mass graves" in the capital Juba.
The grim discovery follows escalating battles between troops loyal to President Salva Kiir and those backing his rival Riek Machar, a former vice president who was sacked in July.
The official toll nationwide has stood at 500 dead for days, although aid workers have said the toll was likely to be far higher.
Witnesses that AFP has spoken to recount a wave of atrocities, including an orchestrated campaign of ethnic mass killings and rape.
In a Christmas message to the people, Mr Kiir said that "innocent people have been wantonly killed", warning that the violence risked spiralling out of control.
"There are now people who are targeting others because of their tribal affiliation... It will only lead to one thing and that is to turn this new nation into chaos," Mr Kiir said in a statement.
The unrest has taken on an ethnic dimension, pitting Mr Kiir's Dinka tribe against the Nuer tribe to which Machar belongs.
UN chief Ban Ki Moon has warned reports of crimes against humanity will be investigated, as well as asking the Security Council to nearly double the size of the UN mission in the country.
However, Mr Machar said for the first time Tuesday that he was "ready" to accept Mr Kiir's offer of talks, suggesting neighbouring Ethiopia as a neutral location.
"We want democratic free and fair elections. We want Salva Kiir to call it a day," Mr Machar said, listing his demands, which follow days of shuttle diplomacy by African nations and calls from Western powers for fighting to stop.
Mr Machar's promise of talks came shortly before the army stormed Bor town, which Information Minister Michael Makwei called a "gift of the government of South Sudan to the people".
Bor's capture, apparently without major resistance by the rebels, relieves some 17,000 besieged civilians who fled into the UN peacekeeping compound for protection, severely stretching limited food and supplies.
UN peacekeepers had spent days bolstering fortifications ahead of the army assault, after militia gunmen last week stormed a UN compound in the Jonglei outpost of Akobo, killing two Indian soldiers and some 20 ethnic Dinka civilians sheltering there.
UN vote on extra troops
======================= Fighting has spread to half of the young nation's 10 states, the United Nations said on Tuesday, with hundreds of thousands fleeing to the countryside and UN bases flooded with others seeking shelter, prompting warnings of an imminent humanitarian disaster.
Mr Pillay's spokesman told AFP that a UN official had on Monday visited a mass killing site in Bentiu, the capital of the oil-rich Unity State, and counted at least 34 bodies with dozens more feared dead.
The UN official who visited counted 14 bodies in the grave and 20 at a riverside nearby, but 74 ethnic Dinka soldiers are also missing feared dead, she said.
Rebel fighters are also reported to have committed atrocities in areas they control.
Late on Tuesday, the Security Council voted to nearly double the number of UN peacekeepers and police.
UN chief Ban Ki Moon had called for the Unmiss force to be increased to counter a major outbreak of violence, and member states agreed to increase the military contingent to 12,500 troops.
A parallel civilian police deployment will reach 1,323.
Council members also demanded an end to hostilities between the rival forces and expressed "grave alarm and concern regarding the rapidly deteriorating security and humanitarian crisis", warning that those responsible for war crimes would be held responsible.
President Kiir has accused Mr Machar of starting the fighting by attempting a coup, while Machar says the president has exploited tensions within the army to carry out a purge.
Speaking from the relative safety of a UN base in Juba, two ethnic Nuer men alleged they were arrested by government soldiers along with an estimated 250 other men, herded into a police station in the capital Juba and then fired on.
"It was horrible, because to survive you had to cover yourself with the bodies of dead people, and... the bodies started to smell really bad," said one of the men, named Simon, who would give only his first name for fear of reprisals.
"We remained only 12 people. The rest were killed off," said Gatwech, another survivor and witness to the alleged massacre, who was also nursing several wounds and recounted similar details.
The government has denied being behind any ethnic violence.