South Sudan's President Salva Kiir is cutting short a trip to China because of what a Chinese official called "domestic issues."
Kiir had planned to remain in the country until Saturday. He met with the National People's Congress chairman Wu Bangguo Wednesday, who said it was unfortunate the South Sudanese leader would be leaving and canceling a trip to Shanghai.
It was not clear when Kiir will depart China. He held talks Tuesday with Chinese President Hu Jintao, and said Sudan's bombings of southern territory amount to a declaration of war against his country.
China has urged both sides to settle their issues through peaceful negotiations, and said it is sending an envoy to the region to promote talks.
Tuesday, the United Nations Security Council 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, noting that the withdrawal of South Sudanese troops (SPLA) 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," Rice said.
The ambassador said the U.N. Mission in South Sudan confirmed the bombings in Unity state killed at least 16 civilians and injured 34 others.
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.
South Sudan's deputy defense minister, Majak D'Agoot said the next few days will be "crucial" to avoiding an all-out war.
The White House condemned Sudan's military incursions into South Sudan, Tuesday. White House spokesman Jay Carney said the United States calls on both governments to agree to an immediate cease-fire and recommit to negotiations.
South Sudan's military has been sending reinforcements to the border with Sudan. Military officials said they were preparing defensive positions to respond to any further provocation from Khartoum.
Sudan and South Sudan have been on the edge of full-scale war after SPLA forces withdrew from Heglig, which they occupied for 10 days earlier this month.
Juba claims the SPLA left the area in response to international pressure, while Khartoum claims it retook control by force.
Sudan's president, Omar al-Bashir, visited Heglig Monday to demonstrate that the territory was under his forces' control.
The two sides had previously fought a 21-year civil war that killed more than 2 million people. The war ended with a 2005 peace agreement that included an independence referendum for the south.