Juba - South Sudan accused Sudan on Monday of flying warplanes over the southern capital Juba and bombing other parts of its territory, one day before the resumption of negotiations between the two foes.
The two Sudans have been at loggerheads over a long list of disputes since the southern nation declared independence in July last year. Fierce clashes on the disputed border raised fears of an all-out war last in April.
"Yesterday the Sudanese air force violated the airspace of South Sudan, including flying over Juba and other towns in South Sudan," the south's chief negotiator Pagan Amum told reporters at Juba airport before leaving for the talks in Addis Ababa.
He described the over-flights as a violation of a May 2 U.N. Security Council resolution that called on the neighbours to end fighting and resume talks or face sanctions.
"Today, as we are leaving to the negotiations, the government of Sudan is attacking South Sudan. Now, as we speak, (the state of) Northern Bahr el Ghazal is under attack by the Republic of Sudan by land and also aerial bombardment is continuing ... (These are) not signs of peace," Amum said.
Sudan's army spokesman al-Sawarmi Khalid could not be reached on his mobile phone. The foreign ministry was also not immediately available for comment.
Sudan routinely denies bombing the South's territory and the remoteness of the border region makes air strikes difficult to verify, although Reuters journalists have witnessed several bombing raids in the South since the country split in two.
Since partition, the two countries have failed to demarcate five areas along their shared border or sign agreements on citizenship, oil transit fees and the division of debt.
Despite the fresh attacks, Amum said he was hopeful the next round of talks in Addis Ababa will prove fruitful because of the surge in international support for an agreement.
Diplomats see no quick progress at the talks as positions seem wide apart. Sudan has said it wants to make security a priority and accuses Juba of supporting rebels in Sudan's borderlands. South Sudan denies the claims.
Both sides also need to agree on how much landlocked South Sudan should pay to export oil through Sudan's Red Sea port of Port Sudan.
In January, South Sudan shut down its entire output of 350,000 barrels a day to stop Khartoum taking some oil for what Sudan calls unpaid export fees. Oil is the lifeblood of both economies.