President Yoweri Museveni has deployed Ugandan special forces troops to support South Sudanese President Salva Kiir’s government as the US warned that the country was on the brink of civil war.

The deployment was made at the request of President Kiir, who is battling to maintain control over the country following a week of violence sparked by an alleged coup attempt in the capital, Juba, but has now spread to other regions.

President Museveni is a key ally of President Kiir, and Ugandan forces fought alongside the Sudan People’s Liberation Army in its war against Khartoum; Khartoum had supported the Lord’s Resistance Army rebel group.

The death toll in the fighting in South Sudan has risen to 500 according to UN sources as the conflict takes on an ethnic angle.

Three Indian peacekeepers were killed in an attack on a UN base in Jonglei by youth believed to belong to the Nuer ethnic group.

The Sudan Tribune newspaper reported that 16 oil workers were killed on Thursday in a clash between rival tribes in Unity State.

President Kiir has denied the existence of ethnic tensions, citing the multi-ethnic identity of the officials arrested in connection with the alleged coup plot.

Former deputy president Riek Machar, whose Nuer tribe is the second-largest in the country, denied backing the alleged coup d’état. In an interview with the BBC, he accused President Kiir, whose Dinka tribe is the most populous and with whom he fell out before his sacking in July, of creating a military crisis in order to get rid of his political opponents.

At least 10 former ministers close to Dr Machar have been arrested since fighting broke out on Sunday night; the whereabouts of Dr Machar remain unclear.

Sources in Juba told The EastAfrican that the former deputy president had checked into the UN Mission to South Sudan (UNMISS) camp in Bor at about 6pm on Wednesday.

Located some 200 kilometres north of Juba, Bor, the capital of Jonglei state, was taken by rebelling Sudanese People’s Liberation Army soldiers under the command of Gen Peter Gadet, who was reported to have switched his loyalty from President Kiir to Dr Machar.

Sources said the former deputy president travelled along the River Nile from Juba to Bor, and checked in at the Korean section of the UN camp. These reports could not be independently verified, and UNMISS denied harbouring any of the “rebel” officials in an earlier statement.

The exact number of Uganda’s special forces deployed to Juba was not immediately known, but sources in Uganda’s military intelligence said the number was in the “low hundreds,” but could be increased depending on the condition of South Sudan.

READ: Ugandan troops deployed in South Sudan capital: report

The special forces flew into South Sudan in a military C-130 transport plane and helped secure Juba International Airport to facilitate the evacuation of foreign nationals.

They were also expected to secure a road corridor from Juba to Nimule, on the border with Uganda, to allow more foreigners to leave by road.

The deployment appears to have been done with the knowledge and understanding of Western missions in the region, which have piggybacked on the operation to fly their nationals out of Juba Airport.

US deployment

US President Barack Obama announced that the US military had deployed 45 combat troops to South Sudan to protect US personnel and assets. Washington temporarily suspended operations at its embassy in Juba, warning of a heightened risk of civil war.

“South Sudan stands at the precipice. Recent fighting threatens to plunge South Sudan back into the dark days of its past,” President Obama said in a letter to the US Congress informing it of his deployment of American troops to the country.

“Inflammatory rhetoric and targeted violence must cease. All sides must listen to the wise counsel of their neighbours, commit to dialogue and take immediate steps to urge calm and support reconciliation.”

READ: Fears of civil war as violence spreads in South Sudan

Although the US forces are armed for combat, American officials said they were in the country with a defensive mandate.

A regional initiative was underway by late Friday to initiate dialogue with the warring parties and seek a political resolution to the crisis. Foreign ministers from the Inter Governmental Authority on Development, which includes Sudan, Ethiopia, Kenya, Somalia, Uganda and Djibouti, are leading the peace initiative.

Led by Ethiopia’s Tedros Adhanom, the foreign ministers were scheduled to meet President Kiir as well as Rebecca Garang Mabior, founding president John Garang’s widow, who is a critic of the sitting president and a political ally of Dr Machar.

The discussions are expected to be tense. President Kiir has publicly expressed his willingness to meet his political rivals, but Dr Machar raised the ante this week when he called for the unseating of the incumbent.

Dr Machar was expected to challenge President Kiir at the next election scheduled for 2015, but there are increasing calls for the creation of a government of national unity and political reforms ahead of the poll.

The current violence follows months of political tension between the two camps. President Kiir’s political opponents, many of whom were purged in a July Cabinet reshuffle over allegations of corruption and abuse of office, have coalesced around Dr Machar and are calling for reforms to lead to a more transparent and accountable government.

The claims of the attempted coup d’état are contested. Sources in the South Sudan military said fighting broke out after an attempt to disarm predominantly Nuer members of the presidential guard.

This followed a stormy meeting of the National Liberation Council, a key organ of the ruling Sudan People’s Liberation Movement party, on Sunday, at which pro-Machar and pro-Kiir factions failed to agree on the composition of a key body that will pick the party’s candidate for the next election.

The pro-Machar officials have been publicly mobilising political support against the incumbent for several months. It is not clear whether the disarmament was in response to a genuine coup attempt or whether it was a pre-emptive strike by President Kiir’s administration following the heated party meeting.

There are fears that the spreading violence could feed into ethnic tensions in the country and turn into a civil war; the country remains heavily militarised and has high levels of internal dissatisfaction.

The government has been fighting a rebel militia linked to David Yau Yau in Jonglei State, and there are fears that he could link up with Gen Gadet leading to a bigger confrontation. Both commanders have links to the administration in Khartoum that go back to the time Dr Machar defected from the SPLA.

Deep suspicions remain within SPLA between the militia fighters once allied with Khartoum and those who stayed with John Garang, President Kiir, and the rest of the establishment of SPLA.

Gen Gadet’s attack on Bor has raised echoes of the 1991 attack on the town by Nuer militia loyal to Dr Machar that claimed at least 2,000 lives.

The ethnic tensions were visible as gunfights broke out on Thursday night in Rubkona and Bentiu, the capital of oil-producing Unity State.

Mabek Lang, the deputy governor of Unity State, told Radio Tamazuj in South Sudan that soldiers deployed in the area divided themselves into different tribal camps in anticipation of clashes.

Additional reporting from agencies