South Sudan is accusing neighboring Sudan of bombing southern targets, days after the two sides signed a non-aggression deal. The allegation threatens already troubled talks on sharing oil revenues.

South Sudan's chief negotiator at the African Union-mediated talks, Pagan Amum, said Sudanese jets bombed an area in the south's Unity state, not far from the two countries' disputed border. He gave few details, saying word of the attack had just been received.

The bombing, if confirmed, would be the first violation of a non-aggression agreement signed Friday at the beginning of a round of talks on oil and other contentious issues. Amum accused Khartoum of continuing its attempts to destabilize the border.

"That is a bad sign that the government of Sudan is not serious to non-aggression, but we expressed our hope the government of Sudan would now end its attacks on South Sudan, particularly areas of bombardment," said Amum.

Speaking to reporters, Amum said the south is continuing to take a tough line on the main issue in the six days of talks - sharing oil revenues. He said any decision to reopen the pipeline that carries southern oil to international markets would only come after Khartoum pays for oil it took from the pipeline while the payments dispute raged last month.

"There is no way for us to resume unless the government of Sudan pays the south the market value of all the oil they have stolen, which is in excess of $500 million. We cannot export our oil if it is not secure and safe, if the government of Sudan are practicing state piracy. It would be dangerous for us to send even one barrel, not millions," said Amum.

South Sudan took the bulk of Sudanese oil when it became independent last year, but the oil must pass through the north to reach Port Sudan on the Red Sea.

Khartoum’s negotiators did not speak to reporters as they left the African Union headquarters, where the two sides briefed the AU Peace and Security Council.

The talks, mediated by former South African president Thabo Mbeki, are expected to carry on through at least Wednesday, but diplomats close to the negotiations say they may be extended if there is any sign of a deal that might open the oil pipeline.

Experts say the pipeline shutdown is costing both countries hundreds of millions of dollars a month in lost revenues.