Soldiers from the United Nations Mission in Sudan.

Soldiers from the United Nations Mission in Sudan. Photo: Reuters

Australia will deploy two military aircraft to South Sudan for United Nations efforts to restore peace to the world's youngest nation.

Acting Prime Minister Warren Truss announced on Thursday that Australia had agreed to a UN request for support to transport personnel and equipment to the war-torn country.

The UN Security Council this week unanimously approved a temporary increase in the strength of the UN mission in South Sudan, from 7000 military personnel and 900 police to 12,500 military personnel and more than 1300 police.

Thousands of South Sudanese have been killed in more than a week of violence following the eruption of the conflict in the capital Juba on December 15.

Mr Truss said the RAAF C-17A Globemaster and C-130 Hercules may also be used to evacuate some of the 45,000 people who are being protected by the UN in the country.

He said the mission was expected to last two weeks, and would not involve any more Australian personnel beyond the aircraft crew. ''We anticipate that this will be a short-term commitment,'' Mr Truss said.

Each aircraft is typically crewed by two pilots and a loadmaster, and Mr Truss did not expect any request for further resources or troops. About 20 Australian defence force personnel are already in South Sudan, though none are serving in combat roles.

The Australians are serving in UN mission headquarters, as military liaison officers and providing aviation and logistical support. A small number of Australian police are also serving in the country.

Australia's contribution to the South Sudan mission represents the 40th UN peacekeeping operation it has taken part in.

Mr Truss said the redeployment of the aircraft, which were conducting routine operations in the Middle East Area of Operations, would not adversely affect any other Australian operations. He acknowledged such operations always carried risks.

Mr Truss urged Australian civilians in South Sudan to leave the country, adding that commercial air services were still available.

Seventy Australians, many working for non-government organisations, have registered their presence in South Sudan with the Department of Foreign Affairs and Trade. A further 230 have already left the country.

But the government believes there are up to 1000 other Australians, many of whom are dual nationals, who have not registered their presence in South Sudan with Australian authorities.