South Sudan rebel leader Riek Machar confirmed Friday that rebel forces had lost control of the key northern oil town of Bentiu, but vowed his fighters would continue their battle against the government.

"We withdrew from Bentiu, but it was to avoid fighting in the streets and save civilian lives. We fight on, we will continue the battle," Machar told Agence France Presse by satellite telephone from an undisclosed location in the country.

The U.N. Office for the Coordination of Humanitarian Affairs said Wednesday it was preparing for the arrival of some 10,000 South Sudanese refugees expected to enter Sudan's troubled Darfur region.

"Humanitarians in East Darfur are preparing to respond to a possible influx of an estimated 10,000 people from South Sudan," the weekly OCHA bulletin said.

Thousands of African asylum seekers demonstrated in Tel Aviv on Tuesday for a third straight day of protests against Israel's immigration policies.

Migrants, most of them fleeing Eritrea or Sudan, held banners that read "We are refugees," and "No more prison," as they marched on Western embassies and the offices of the U.N. refugee agency (UNHCR).

Sudan's President Omar al-Bashir arrived Monday in Juba calling for an end to three weeks of fighting in South Sudan as mediators struggled to get peace negotiations under way in neighboring Ethiopia.

There were reports meanwhile of ongoing fierce clashes near the rebel-held town of Bor, situated 200 kilometers (130 miles) north of the capital Juba, with South Sudan's army pouring in reinforcements in a bid to recapture the area.

Sudan's President Omar al-Bashir will visit South Sudan Monday, state radio said, as negotiators in Ethiopia prepared formal ceasefire talks over three weeks of fighting in the world's youngest country.

Radio Omdurman said Sunday that Bashir would meet his southern counterpart, President Salva Kiir, in Juba for talks on the conflict in South Sudan, without giving further details.

The chief negotiators for South Sudan's government and rebels held another face-to-face meeting on Sunday in preparation for the start of formal ceasefire talks between the two sides, officials said.

A spokesman for the rebel team said their delegation leader, Taban Deng, met in the Ethiopian capital with Nhial Deng Nhial, head of the government negotiation team.

South Sudan's warring parties were Wednesday set to begin peace talks in Addis Ababa aimed at bringing an end to a nearly three-week-old civil war that has already left thousands dead.

Government and rebel negotiating teams both arrived in the Ethiopian capital by Wednesday evening, a source close to the talks said and diplomats said they expected formal discussions on a possible ceasefire to begin on Thursday, although informal contacts may take place later Wednesday.

International efforts to bring peace to strife-torn South Sudan appeared at an impasse Sunday as the government accused former vice president Riek Machar of recruiting tens of thousands of fighters.

As the fighting which is believed to have killed thousands moves towards a third week, Juba claimed that Machar, the de facto leader of rebels fighting the government, has recruited up to 25,000 young men from his Nuer tribe in the eastern state of Jonglei who it says are "ready to attack any time".

U.N. Secretary General Ban Ki-moon has reiterated a call for perpetrators of violence in South Sudan to be brought to justice.

"All violence, attacks and human rights abuses must end immediately," Ban's spokesman said in a statement late Saturday.

Hundreds of South Sudanese have fled across the border into neighboring Sudan, a source at the U.N. refugee agency said Saturday, after fierce fighting in the world's newest state.

"According to information received by the UNHCR that has not been confirmed, hundreds of citizens of South Sudan have crossed the border into Sudanese territory from several border areas," the source told Agence France Presse on condition of anonymity.