Khartoum forces 'bomb South Sudan town'
South Sudan has accused Sudan of launching further bombing raids on its territory and against its forces.
The governor of Unity state says several people were killed in its capital Bentiu when a plane dropped bombs on a market.
South Sudan also says its troops came under air attack in the oil-producing Heglig region which they have seized.
Sudan's ambassador to the UK, Abdullahi Al Azreg, said Sudan did not target civilians.
He insisted Khartoum had bombed military camps used by northern rebels supported by South Sudan.
"These people are occupying our land. Everybody is witnessing what they are doing. They have killed the civilians, they are doing very bad things. We will target the rebels as long as they are occupying our land," he told the BBC.
South Sudan said earlier on Saturday that it had repulsed an offensive on its positions near Heglig.
Vice-President Riek Machar said the ground fighting took place on Friday 30km (18 miles) north of Heglig.
South Sudan seized the oil field on Tuesday, sparking international condemnation and fears of a wider war with its northern neighbour.
South Sudan entered the oil field in response to what it said were attacks from north of the border.
Sudan's leaders are furious after its southern neighbour took over the Heglig oilfield, which is internationally accepted as Sudanese territory.
The African Union has demanded an unconditional withdrawal.
The South seceded nine months ago in a deal that ended decades of civil war, but there remain a number of major disputes, including oil.
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Sudan's army confirmed on Friday it was launching attacks to retake Heglig after the Khartoum government vowed to react with "all means" against the offensive by South Sudanese forces.
And Sudanese army spokesman Col Sawarmi Khalid said on Saturday Heglig region was "100%" under their control.
"We are now inside Heglig and we can talk about a few kilometres separating us from the Heglig oilfield."
But Mr Machar told the BBC his country's soldiers had now pushed Sudanese troops back to Karasana, north of Heglig.
South Sudanese Information Minister Barnaba Marial Benjamin told Reuters on Saturday: "They tried to attack our positions north of Heglig last night but it was contained. Heglig is [still] under our control."
South Sudan's military spokesman, Col Philip Aguer, told Agence France-Presse two Sudanese tanks had been destroyed.
There is no independent confirmation of the South's claims.
The BBC's James Copnall, in Khartoum, says it seems likely there will be further battles and what started out as a border skirmish now seems perilously close to becoming an all-out war.
Heglig is vital because it accounts for about half of Sudan's 115,000 barrel-a-day oil output and the fighting has stopped production there.
The African Union's Peace and Security Council has called the occupation of Heglig "illegal and unacceptable", but also condemned Sudan for carrying out aerial bombardments of South Sudan.
On Thursday, the UN Security Council called for an "immediate" ceasefire and expressed "deep and growing alarm at the escalating conflict".