A senior UN human rights official warned Wednesday of the risk that full-blown war may break out again between north and south Sudan if clashes in the border areas spread.

Fighting between north Sudan's military and elements linked to the South Sudan People's Liberation Army, or SPLA, has persisted along the provisional border ahead of the south's formal secession July 9. The conflicts centre on long-standing ethnic disputes, but also on access to cattle-grazing areas and the future of the oil-rich region of Abyei, in what is currently part of north Sudan's South Kordofan state.

"If this renewed fighting in border areas doesn't stop and it further spreads to other areas of South Kordofan and Blue Nile, then obviously it's war again," said Kyung-wha Kang, the UN Deputy High Commissioner for Human Rights.

Northern forces appeared little concerned with maintaining law and order in Abyei when Kang travelled to the main settlement there last week, he said.

"I was able to visit Abyei, which is a scene of total destruction as far as we could see," she told reporters in Geneva. "We saw looters still removing what little remained of the village and loading them onto trucks under the watch of the Sudanese armed forces and others who appeared to be militia."

Reports of civilians abused

Kang called for an investigation into what happened at Abyei, and also in the South Kordofan capital of Kadugli, to the northeast, where the UN has received reports of civilians being abused after they were forced by north Sudan authorities to leave a UN-protected compound last week.

Kang said she was denied access to Kadugli to learn what happened to some 7,000 ethnic Nuba, who were ordered to leave the compound June 20 by people posing as Sudanese Red Crescent workers. UN staff haven't been able to contact the civilians since.

"There are lots of very, very serious allegations" about what happened in Kadugli in recent weeks, Kang said. So far, her office hasn't been able to confirm claims that civilians were killed in large numbers.

Kang also voiced concern about the situation in South Sudan, noting that at least 1,400 civilians have been killed there this year. She said the killings appeared to be partly to blame on badly trained SPLA fighters.

Sudan's president visits China

Meanwhile, Sudan's president, who is wanted on a war crimes warrant, won pledges Wednesday from China and its state-owned energy firm that they will continue investing in his country after its resource-rich southern region becomes independent next month.

Chinese President Hu Jintao, left, and Sudan's President Omar al-Bashir met Wednesday despite an international warrant accusing al-Bashir of war crimes. Liu Jin/Associated Press

Sudan's Foreign Minister Ali Ahmed Karti said Wednesday that President Omar al-Bashir came to China hoping to hear Sudan's biggest diplomatic and economic backer would continue to invest in northern Sudan's oil, agriculture and mining sectors.

"We had good assurances from his excellency President Hu Jintao that China would go on working with Sudan hand in hand whether politically or financially or economically," Karti said.

Karti also said al-Bashir also visited the Beijing headquarters of China National Petroleum Corp., Asia's biggest oil and gas producer by volume, and was assured the state-owned firm would continue to invest in the north.

CNPC, which made a 20-year, multibillion-dollar development deal with Sudan in 2007, signed an agreement Tuesday with the government to boost co-operation. A company statement did not give details.

South Sudan's declaration of independence will be the culmination of a 2005 peace deal that ended more than two decades of civil war that killed more than 2 million people.