U.S. President Barack Obama warned that South Sudan stands at the "precipice" of renewed civil war, amid spiraling violence including an attack on a U.N. base that killed three Indian peacekeepers.

The United Nations Security Council readied emergency consultations on the the rapidly fledgling nation Friday, amid growing fears the country was sliding towards greater civil strife.

At least five South Sudanese workers were killed after attackers stormed their compound in the key Unity oil field, an official in the Chinese-owned company said Thursday, amid wider violence wracking the young nation.

"A group of armed men came to the compound and killed staff" late on Wednesday, a senior official at the Greater Nile Petroleum Operating Company (GNPOC) said, not wanting to give his name as he was not authorized to speak to the media.

The last Sudanese prisoners to be released from U.S. detention at Guantanamo Bay arrived home Thursday, as U.S. President Barack Obama tries to speed up repatriations and close the controversial facility.

U.S. military personnel helped Mohammed Noor Uthman and Ibrahim Othman Ibrahim Idris onto the exit stairway of a U.S. Air Force transport plane after it landed in Khartoum.

Clashes between rival army factions in South Sudan have left up to 500 dead and 800 wounded, a top U.N. official told the U.N. Security Council on Tuesday.

The United Nations has been told by local hospitals that between 400 and 500 people have been killed in South Sudan's capital since Sunday, U.N. peacekeeping chief Herve Ladsous told the council, according to diplomats who attended a private briefing with him.

The African Union said Tuesday it was "deeply concerned" about events in South Sudan following two days of deadly fighting in the young nation, and urged restraint.

The AU "urges the government and leadership of South Sudan and all other stakeholders to exercise maximum restraint and avert any further escalation," the head of the AU's executive council, Nkosazana Dlamini-Zuma, said in a statement.

The United States Tuesday ordered non-essential embassy staff out of South Sudan as fresh battles raged between rival troops in unrest that has already killed 73 soldiers and sent thousands of terrified civilians fleeing since an alleged coup bid.

The fighting in the world's youngest nation has set off alarm bells in the international community, with the United Nations urging the warring groups to refrain from ethnic violence.

Sudan's new cabinet on Monday approved a budget ruling out price increases, after the slashing of fuel subsidies in September led to the worst urban unrest of President Omar al-Bashir's regime.

"This budget will not include increases in taxation, nor will it raise other prices," Finance Minister Badereldien Mahmoud told reporters after ministers endorsed the 2014 budget.

Almost two million people are displaced in Darfur, the U.N.'s top official in Sudan said on Monday, giving a new figure for the region where violence has worsened this year.

"We estimate that the internally displaced people... are close to 1.9 million, and that there are 1.3 million non-IDP's who are severely affected and/or food insecure," Ali Al-Za'tari said in the capital of North Darfur state.

Three people were wounded Saturday when shells struck the capital of Sudan's war-torn South Kordofan state, where fighting has escalated, residents and officials said.

Rebels of the Sudan People's Liberation Army-North (SPLA-N), fighting since 2011 in South Kordofan, have periodically shelled Kadugli since late last year.

The medical needs of 165,000 Sudanese children are being held "hostage" by the warring parties in South Kordofan and Blue Nile states, a senior United Nations official said on Thursday.

Those children "are not accessing basic health services, including vaccination against measles and polio", Martin Mogwanja, deputy executive director for operations at the U.N. children's fund (UNICEF), told reporters after a four-day visit to Sudan.