JUBA/KHARTOUM South Sudan said the Sudanese air force bombed key oil fields in a cross-border raid on Tuesday, one day after a rare direct confrontation between the two countries.
Clashes broke out on Monday in several places along the poorly-marked border in some of the worst fighting between the two armies since South Sudan became independent in July under a 2005 peace agreement.
The violence prompted Sudan's President Omar Hassan al-Bashir to suspend a trip to Juba to meet his southern counterpart Salva Kiir to tackle a long list of disputes, according to Sudan's state radio.
The two countries have been at loggerheads since the South became independent, taking away three-quarters of the oil production -- the lifeline of both economies. Sharing oil wealth is at the heart of the bitter conflict.
South Sudan on Tuesday accused Khartoum of sending Antonov warplanes to bomb the main oil fields in Unity state near the Sudan border.
"This morning as you called I heard the Antonov hovering over Bentiu town because it has just dropped some bombs in the main Unity oil fields," Unity state Information Minister Gideon Gatpan told Reuters.
"It has now gone back, possibly for refuelling, and may come back," he said by telephone.
Sudanese army spokesman Sawarmi Khaled Saad could not be reached on his mobile phone but Asian oil group GNPOC - the Greater Nile Petroleum Operating Company, a consortium led by China's CNPC - confirmed the bombing.
"The warplanes are hovering everywhere ... One bomb actually just missed Unity base camp but anywhere else so far there is no information," said Vice President Chom Juaj.
"They bombed the oil field but so far we are still waiting for the report from the field telling us if they are damaged or not," he said.
Both sides blamed each other for having started the fighting on Monday. Events in the 1,800 km (1,100 miles) long border area are hard to verify as much of the territory is disputed and not accessible for journalists.
Sudan accused South Sudan of having attacked the Heglig border area where a large oil field is under Khartoum's control. The South said its army had only chased Sudanese ground forces there in self-defence after they had launched an attack on southern territory.
The new violence ends a recent rapprochement between the neighbours which had made some progress this month in talks sponsored by the African Union trying to end the bitter dispute.
Both countries have been unable to agree how much the landlocked South should pay to export its crude through Sudan, prompting it to shut down its production after Khartoum started taking some oil as what it calls unpaid transit fee.
Khartoum and Juba earlier this month had reached two agreements on free movement of citizens in each other's territory, a step that had given hope that an oil deal was also possible during the presidents' meeting.
But Sudan's Information Minister Abdallah Ali Masar questioned the recent agreements, accusing Juba of playing tricks at the negotiation table.
"The agreements in Addis Ababa and a visit of a southern delegation (on Friday) to Khartoum was only swindle and manipulation," he told state news agency SUNA late on Monday.
Officials in Khartoum could not be immediately reached to confirm that Bashir's visit to Juba had been suspended as reported by Sudanese radio and newspapers.
Each country has accused the other of supporting rebels on either side of the border but direct confrontations are rare.
Sudan's army and SPLM-North rebels have been fighting in South Kordofan since June. Clashes spread in September to Sudan's Blue Nile state which also borders South Sudan.
Both South Kordofan and Blue Nile are home to large communities who sided with the south during the civil war but were left on the Sudan side of the border after the secession. Khartoum says the SPLM-North is supported by South Sudan, an accusation dismissed by the southern government.
The U.N. refugee agency UNHCR said it was worried about the safety of 16,000 refugees in Yida camp near the border where fighting was reported on Monday.
"It is very close to Yida, that is why we are concerned," UNHCR spokeswoman Fatoumata Lejeune-Kaba told Reuters.
(Reporting by Hereward Holland and Ulf Laessing; additional reporting by Ulf Laessing; Editing by Louise Ireland)