United Nations secretary-general Ban Ki-moon has condemned Sudan's bombardment of a market in the capital of South Sudan's oil-producing Unity State and urged Khartoum to stop fighting.
"The secretary-general condemns the aerial bombardment on South Sudan by Sudanese Armed Forces and calls on the government of Sudan to cease all hostilities immediately," Mr Ban's press office said in a statement.
"[Mr Ban] reiterates that there can be no military solution to the disputes between Sudan and South Sudan," it said.
Sudan denied carrying out any air raids but its president Omar Hassan al-Bashir ramped up the political tension by ruling out a return to negotiations with the South, saying its government only understood "the language of the gun".
A Reuters journalist saw aircraft dropping two bombs near a bridge linking two areas of Unity's capital Bentiu, although it was not possible to verify the planes' affiliation. He saw market stalls ablaze and the body of one child.
Weeks of border fighting have brought the neighbours closer to a full-blown war than at any time since South Sudan split from Sudan as an independent country in July.
The two territories went their separate ways last year without settling a list of bitter disputes over the position of their shared border, the ownership of key territories and how much the landlocked South should pay to transport its oil through Sudan. The disputes have already halted nearly all the oil production that underpins both struggling economies. "Bashir is declaring war on South Sudan. It's something obvious," southern army (SPLA) spokesman Philip Aguer said after the Bentiu bombing.
Mr Aguer and the United Nations Mission in South Sudan said two people were killed in the air strike in Unity state where the Greater Nile Petroleum Operating Company (GNPOC) operates blocks. China's CNPC leads this consortium, along with Malaysia's Petronas and India's ONGC Videsh.
"These indiscriminate bombings resulting in the loss of civilian lives must stop," said Hilde F Johnson, special representative of the secretary-general for South Sudan.
The mission said its officers had seen one bomb land on the market and three near a bridge. "A young boy burned to death as the hut he was in caught fire from the blast in Rubkona market area," it quoted one of its officers as saying.
Bentiu is about 80km from the contested and poorly marked border with Sudan.
Sudan denied carrying out any air attacks in the area. "We have no relation to what happened in Unity state, and we absolutely did not bomb anywhere in South Sudan," the country's military spokesman, Al-Sawarmi Khalid, said.
In the worst fighting since the split, South Sudan earlier this month seized the disputed oil-producing territory of Heglig - then announced it had started withdrawing on Friday, following sharp criticism from the UN secretary-general.
Mr Bashir, dressed in military uniform, visited the Heglig region yesterday..
Speaking to Sudanese army troops, he vowed not to negotiate with South Sudan after it had occupied the region. "We will not negotiate with the South's government, because they don't understand anything but the language of the gun and ammunition," he said at a barracks near the oilfield along the contested border.
Reuters