China has called for an immediate end to hostilities in South Sudan, where the government is in talks with neighbouring Sudan to deploy a joint military force to protect vital oilfields from rebels.

In a rare overt political intervention in Africa, the Chinese foreign minister, Wang Yi, said he was deeply concerned by the unrest in South Sudan, which has left more than 1,000 people dead and reduced oil flows by about a fifth.

"China's position with regards to the current situation in South Sudan is very clear," Wang told reporters in Addis Ababa, Ethiopia, where direct talks aimed at a ceasefire finally got under way on Monday. "First, we call for an immediate cessation of hostilities and violence."

China would do what it could to help restore stability in South Sudan and urged international powers to back the Ethiopian-led mediation efforts. An Ethiopian delegate told Reuters that Wang met both rebel and government delegations. China is Africa's single biggest trading partner, having overtaken the United States over the past decade, but professes to remain neutral and not interfere in African states' internal politics.

It is the biggest investor in oilfields in South Sudan through state-owned Chinese oil groups China National Petroleum Corp (CNPC) and Sinopec. The fighting forced CNPC to evacuate workers.

Similar in size to France, South Sudan is estimated by BP to hold sub-Saharan Africa's third biggest oil reserves. Its plight is attracting more global attention than most conflict-torn African nations. US president Barack Obama received daily briefings while on holiday in Hawaii, the New York Times reported, describing this as "a level of attention unheard-of for any other crisis in that part of Africa".

The high stakes were becoming increasingly apparent as Sudanese president Omar al-Bashir flew into Juba to meet his South Sudan counterpart Salva Kiir, less than two years after the governments almost went to war over oil.

Bashir's arrival reflected Sudanese fears that the three-week conflict could damage its struggling economy. All of landlocked South Sudan's oil is piped through its northern neighbour, providing vital hard currency in transit fees for Khartoum.

Sudan's foreign minister Ali Karti said the men were "in consultations about the deployment of a mixed force to protect the oilfields in the south". Neither of the presidents referred to the proposal during a press conference in the South Sudanese capital Juba. The return of Sudanese troops to the south could send the crisis in an unpredictable new direction; at least two million people died during the north-south conflict that eventually led to the south's independence.

Anti-government forces loyal to rebel leader Riek Machar control the town of Bentiu, the capital of oil-rich Unity state. The south's government has said oil is no longer flowing from Unity's fields. Most, if not all, of the Chinese and Pakistani oil workers have left the country because of the outbreak of violence.

Bashir, an indicted war crimes suspect wanted by the international criminal court, would not meet Machar, al-Jazeera reported. It said the Sudanese government attributed this to practical reasons and was not taking sides.

Kiir and Machar were comrades during the south's struggle against Khartoum, which culminated in a US-funded referendum and secession in July 2011. Relations with Sudan had remained fraught and renewed war seemed possible. But in March the two countries agreed to resume pumping oil through pipelines from south to north. A month later Bashir made his first visit to the south since it gained independence.

On Monday Bashir said he feared that after allowing South Sudan to hold a vote to break away from Sudan in 2011, the outbreak of violence could mean "that our huge sacrifice did not bear fruit."

"We have come to see what we can do to stop this war knowing all too well that armed conflict would never resolve a problem and also knowing that any problem no matter how complicated can be solved at the negotiation table," Bashir said. "We fought each other for 20 years and in the end we sat and talked peace. Any further fighting is just a perpetuation of suffering for innocent civilians and loss in of lives and more destruction."

He added: "We are convinced that armed conflict will only create complications that will do no good that the people (of South Sudan) must and will come back to the negotiating table."

Kiir told reporters that "taking power by military force is a crime" and that Machar's actions should be condemned by the international community.

Despite the international pressure from multiple sides, the violence goes on. Fighting continues outside the flashpoint town of Bor, the capital of Jonglei state, which has untapped oil reserves. On Sunday a South Sudanese army general was killed when a government convoy was ambushed.

Meanwhile Oxfam reiterated its warning of a growing humanitarian crisis, noting that the Awerial refugee camp on the banks of the Nile is now home to 75,000 people. Desire Assogbavi, head of the charity's African Union liaison office in Addis Ababa, Ethiopia, said: "Thousands of families already living in extreme poverty have been pushed from their homes and cut off from what they need to survive.

"We are doing what we can to ensure those most affected by the violence have their basic needs met, such as access to food, water and sanitary living conditions. But if the conflict continues, it will become even more difficult to meet the increasing needs of those affected."

Kiir has blamed his long-term rival and former vice-president, Machar, whom he sacked in July, for starting the fighting in a bid to seize power. Machar dismissed the allegation but has acknowledged leading soldiers battling the government.

The conflict has taken on ethnic undertones: Kiir is from the majority Dinka community and Machar from the Nuer group.