South Sudan President Salva Kiir is cutting short a trip to China as fighting along the border with Sudan raises the threat of a full-scale war.

China National People's Congress Chairman Wu Bangguo says it is unfortunate Mr. Kiir would be canceling a trip to Shanghai due to what he called “domestic issues.”

Mr. Kiir was to remain in China until Saturday, but it is unclear when he will depart. On Tuesday, the South Sudanese leader held talks with Chinese President Hu Jintao, and said Sudan had “declared war” against his country.

China has urged both sides to settle their issues peacefully, and says it is sending an envoy to the region to promote talks.

The U.N. Security Council has called for an immediate end to fighting between Sudan and South Sudan.

The U.S. ambassador to the United Nations, Susan Rice, said U.N. officials briefed the Security Council on Tuesday, noting the withdrawal of South Sudanese troops from the oil town of Heglig was initially encouraging, but has resulted in increased bombings by Sudan.

“Council members welcome the withdrawal from Heglig by the SPLA, demanded an immediate halt to aerial bombardments by the Sudanese Armed Forces and urged an immediate cease-fire and a return to the negotiating table.”

Ambassador Rice said the U.N. Mission in South Sudan confirmed the bombings in Unity State killed at least 16 civilians and injured 34 others.

Also Tuesday, the African Union gave the two countries 90 days to settle their disputes over oil, citizenship and boundary issues or face binding international arbitration.

In Washington, the White House called for both governments to agree to an immediate cease-fire and recommit to negotiations.

South Sudan's deputy defense minister, Majak D'Agoot, told VOA the next few days will be “crucial” to avoiding an all-out war.

The two sides previously fought a 21-year civil war that killed more than two-million people. The war ended with a 2005 peace agreement that eventually led to independence for the south.