South Sudan's president will cut short his visit to China amid violence between the world's newest nation and Sudan, officials said Wednesday, as Beijing unveiled plans to send a peace envoy.

The announcements came as China played host to a delegation from its long-time ally Khartoum at the same time as South Sudan President Salva Kiir was in Beijing on an official visit.

China has been a key ally and the largest economic partner of diplomatically isolated Sudan.

But recent clashes have forced a Chinese juggling act to maintain support for Khartoum while not alienating newly founded South Sudan, which is rich in oil.

South Sudan provided some five percent of China's oil until it shut down production in January over a dispute with its neighbour over trans-shipment fees.

Chinese foreign ministry spokesman Liu Weimin told reporters Zhong Jianhua -- China's special representative on African affairs -- would visit the two countries to "promote peace talks". He gave no further details.

Weeks of border hostilities have seen South Sudan -- which gained independence last July -- seize Sudan's most important oil field in the Heglig area on April 10 and hold it for 10 days.

In the latest bout of violence at least 16 civilians were killed and 34 others wounded in Sudanese air raids on its neighbour's Unity state.

The curtailment of Kiir's visit to China was confirmed by Wu Bangguo, nominally the second-ranking Chinese leader, during a meeting between the two men in Beijing.

"It is unfortunate that you have to shorten your stay in China due to domestic issues and are not going to Shanghai," Wu told Kiir as the two men began talks in the presence of journalists.

The visit, which started Monday, was scheduled to last until Saturday and was to have included a trip to China's commercial hub. There was no indication when Kiir would leave the country.

Wu, China's top lawmaker, also told Kiir during the meeting that Beijing supported South Sudan's efforts to develop its economy and pledged cooperation, Chinese state television reported.

Separately, a top Communist party official on Wednesday met a senior official of Sudan's ruling party and hailed "lasting and extensive friendship", the official Xinhua news agency said.

China "supports Sudan in protecting its national sovereignty," Wang Gang, a member of China's powerful politburo, was quoted as telling Ibrahim Ghandour of Sudan's National Congress Party.

The report, which described the visit as a party-to-party exchange, made no direct mention of the conflict, but Chinese officials have repeatedly called for the two sides to halt fighting.

Speaking Tuesday, Chinese President Hu Jintao called on both South Sudan and Sudan to remain calm and resolve the conflict through peaceful negotiations. In his meeting with Hu, Kiir accused Khartoum of declaring war on his country.

Analysts say China will continue pushing for dialogue despite the worsening situation which has showed the limitations of China's traditional policy of "non-interference".

The current fighting is the worst since South Sudan won independence after a 1983-2005 civil war in which about two million people died.