(CNN) -- South Sudan's president, who accused Sudan of declaring war on his nation, cut short his trip to China on Wednesday as tension between the two neighbors intensified over border and oil disputes.
President Salva Kiir canceled the Shanghai leg of his trip. He had planned a five-day trip, ending Saturday.
It's unclear how soon he will return home.
During a visit to Beijing on Tuesday, Kiir accused Sudan of declaring war on his nation.
The visit came at a "critical moment ... because our neighbor in Khartoum has declared war" on South Sudan, Kiir told his Chinese counterpart, Hu Jintao.
His accusation marked the latest in fiery war rhetoric that has drawn alarm and condemnation from the international community.
China, a crucial trading ally to both nations, urged restraint and negotiation, and said it plans to send its envoy for Africa to Sudan and South Sudan to promote peace talks.
Beijing has deep trade ties with Africa, and has had diplomatic and economic ties with Sudan for decades. Ambassador Zhong Jianhua traveled to both countries earlier this year for mediation, the Chinese foreign ministry said.
South Sudan split from Sudan last year as part of a 2005 peace deal that ended decades of war in Africa's largest nation. The war left 2 million people dead and ended with the peace agreement that included an independence referendum for the south.
Despite the split in July, unresolved issues remain between the two, including status of their citizens, division of national debt, disputed border areas and sharing of oil wealth.
Simmering tensions peaked this month when South Sudan seized the oil-producing region of Heglig from Sudan, raising the stakes by targeting a resource that fuels the economies of both nations.
Heglig oil facilities account for about half of Sudan's production of 115,000 barrels a day.
Sudan claims ownership for the region, and lodged complaints with the United Nations and the African Union to pressure South Sudan to withdraw troops from its territory.
The African Union on Tuesday gave the nations 48 hours to cease their hostilities and three months to complete negotiations on outstanding issues or face "appropriate measures."
It said it will seek updates on the status of negotiations and will require compliance by Sudan and South Sudan. Failure to resolve their disputes will lead to an arbitration process, the body said, without getting into specifics.
Heglig is on the border created when the two countries split. While it is a disputed region, Sudan continued administering it after South Sudan declared independence from the north.
"We have every right to use all military means inside our territory to crush the enemy, " said Daffa-Alla Ali Osman, Sudan's ambassador to the United Nations. "Setting territories inside our borders as theirs ... this is a call for war until they stop and refrain from any behavior against the territorial integrity of Sudan."
After an international outcry, including from U.S. President Barack Obama, who urged the nations to resolve their issues peacefully, South Sudan withdrew its troops Saturday and Sudan retook control of Heglig.
"We wish to see a return to peace with our neighbors. We stand by the values of having two states viable and living in peace side by side," said Agnes Oswaha, the South Sudan ambassador to the United Nations.
A day after South Sudan withdrew from the disputed region, it accused Sudan of launching ground and aerial attacks on its territory.
The bombing in Unity state killed at least 16 and left 34 injured, the United Nations said.
U.N. peacekeeping officials in South Sudan confirmed the casualties from bombings near the border, said Susan Rice, the U.S. ambassador to the United Nations and the current Security Council president.
Council members have "demanded an immediate halt to aerial bombardment by the Sudanese armed forces and urged an immediate cease-fire and return to the negotiating table," she said Tuesday.
A spokesman for the Sudanese military could not be immediately reached for comment. Claims from both sides are difficult to confirm because journalists and independent observers do not have access to the front lines.
The international community has appealed for both sides to silence their weapons and return to the negotiating table, with Sudan facing the latest criticism for bombing Bentiu, which is about 60 miles (nearly 100 kilometers) from Heglig.
Last week, Sudanese President Omar al-Bashir vowed to never give up the disputed region, whose loss would send the nation's economy reeling.
Sudan's oil industry suffered when fighting in Heglig halted oil production in those fields.
The Satellite Sentinel Project released images this week suggesting a critical part of the oil pipeline infrastructure was destroyed. The collection manifold, which allows oil flows to be separated or combined without interrupting the flow, appears to have been damaged by an explosion.
Analysts could not determine whether the destruction was the result of ground fighting or aerial bombardment, said Jonathan Hutson, a spokesman for the project, which is led by the Harvard Humanitarian Initiative.
Serious damage to the facility would prevent companies from resuming production and would require substantial investment to repair or rebuild.
CNN's Eunice Yoon contributed to this report from Beijing