The United Nations' top humanitarian official in South Sudan told reporters in the capital, Juba, on Tuesday, that the death toll was much higher than the figure of 500 that officials have given for the past few days.

"Absolutely no doubt in my mind that we're into the thousands" of dead, Toby Lanzer said.

Mass graves found

Meanwhile, UN officials have revised downward the number of corpses found in mass graves on Tuesday.

Ravina Shamdasani, UN human rights office spokesperson in Geneva, said investigators had found 14 bodies in a mass grave in the town of Bentiu, with another 20 at a nearby site. She also said 75 others were missing and feared dead. The office had previously put the number of corpses found at 75.

South Sudan's minister of information, Michael Makeuei Lueth, laid the the blame at the feet of the rebels, saying Bentiu was under their control.

The victims are reported to have been members of the ethnic Dinka group who had been part of the government's forces, the Sudan People's Liberation Army.

Earlier, Navi Pillay, the UN High Commissioner for Human Rights, called on the leaders of both sides of South Sudan's ethnic divide to renounce violence, as civilians were being caught up in the cross-fire.

"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 statement said, also referring to the other major ethnic group at the heart of the violence.

Also on Tuesday, government forces claimed to have retaken the town of Bor from the rebels.

"Forces loyal to the government have taken Bor and [are] now clearing whatever forces that are remaining there," President Salva Kiir told reporters at his office in Juba.

Security Council vote

Meanwhile, the UN Security Council has voted to temporarily raise the number of peacekeepers deployed to South Sudan from the current 7,000 to 12,500, an increase of around 80 percent. The resolution, which was adopted unanimously at a meeting at UN headquarters in New York on Tuesday, will also increase the number of international police officers in the country to just over 1,300 from the current 900.

The additional troops and police officers are to be drawn at least in part from UN missions in the Democratic Republic of Congo, Ivory Coast, Abyei, and Liberia.

The Council also condemned the bloodshed in South Sudan and called for "an immediate cessation of hostilities and the immediate opening of a dialogue."

Attempted coup

Tensions have escalated in South Sudan since December 15, when the country's former vice president, Riek Machar, was alleged to have attempted a coup. Machar has denied responsibility, but has still called on President Kiir to resign. The duo are long-time rivals, with Kiir having ousted Machar as vice president back in July. The two are also split along ethnic lines; Kiir belongs to the Dinka group, while Machar is a Nuer.

Both have expressed a willingness to hold talks to try to end the violence, but so far no meeting has been scheduled.

pfd/ph (AP, AFP, dpa, Reuters)