[BBC.CO.UK] Thousands of people must have been killed in the past week of violence in South Sudan, the top UN humanitarian co-ordinator there has told the BBC. Toby Lanzer, who is in Bentiu in northern Unity state, said it had been "a devastating week for South Sudan".Earlier President Salva Kiir said his forces had recaptured the key town of Bor days after it was seized by rebels.
The rebels are led by Riek Machar, of the ethnic Nuer, who has been battling President Kiir, of the Dinka.
The UN earlier said that it had reports of at least three mass graves. One was in Bentiu in the north, and two in the capital, Juba.
'Palpable fear'
Mr Lanzer told the BBC's Newshour programme: "I think it's undeniable at this stage that there must have been thousands of people who have bit the dust.
"When I've looked at the hospitals in key towns and I've looked at the hospitals in the capital itself, the range of injuries, this is no longer a situation where we can merely say it's hundreds of people who've bit the dust."
Mr Lanzer also said that the number of people seeking shelter from the fighting was "tens of thousands if not hundreds of thousands".
He said that the tensions between different communities in South Sudan was even evident within a UN base he had just visited where some 7,500 people are seeking protection.
"There have been some - to put it diplomatically - very lively discussions and there has been a little tension at times," he said.
"We are managing the situation and I have just had a discussion with the community leaders inside our base where I said to them, for the benefit of all the women and kiddies, and you who are here, we are counting on you to keep it as calm as possible."
The UN High Commissioner for Human Rights, Navi Pillay, said: "There is a palpable fear among civilians of both Dinka and Nuer backgrounds that they will be killed on the basis of their ethnicity."
The UN says at least 80,000 people have been displaced by the South Sudan crisis - about half of them seeking shelter at a number of UN bases.