JUBA/KHARTOUM South Sudan said Sudan attacked it with aerial bombing raids and ground artillery on Monday and Tuesday, accusing Khartoum of trying to sabotage international efforts for peace talks which the African Union hopes to restart next week.
Juba said its armed forces could retaliate if Sudan made further assaults, raising the prospect of a return to the fighting which the United Nations and the AU are seeking to prevent.
The two armies fought in border skirmishes last month after disputes over oil exports and border demarcation boiled over, following South Sudan's birth as an independent nation in July.
The attacks on Monday and Tuesday targeted the area of Werguet, about 30km (19 miles) inside South Sudan's territory in Northern Bahr Al Ghazal state, officials told a news conference.
Sudan's army spokesman, al-Sawarmi Khalid, could not be reached on his mobile phone. There was no immediate independent confirmation of South Sudan's allegations, and limited access to remote border areas makes such verification difficult.
South Sudanese Information Minister Barnaba Marial Benjamin said Sudan's "acts of aggression" violated a May 2 resolution by the U.N. Security Council which ordered both sides to cease hostilities and settle their differences through negotiations or face sanctions.
Juba has accused Sudan of other attacks since May 2.
"This is a slap in the face of the United Nations and the African Union," Benjamin said.
Former South African President Thabo Mbeki, who has been shuttling between Khartoum and Juba as AU mediator in the past few days, said he expected talks between the neighbors to resume next week.
"So the (AU) panel will be convening that meeting next week as agreed by the presidents of two countries," Mbeki said after meeting Sudan's President Omar Hassan al-Bashir in Khartoum. He had met South Sudan's President Salva Kiir on Monday.
"Now we have an agreement between President Bashir and President Salva Kiir that the two panels of negotiation ... they will meet next week and look at all elements of the decision taken by the AU and the U.N. Security Council," he added.
Neither side immediately confirmed a meeting next week.
Barnaba said South Sudan's delegation was ready to fly to Addis Ababa but the question was whether Sudan wanted to talk. "We are ready to talk anytime," he told Reuters.
Ibrahim Ghandour, a senior official in Bashir's National Congress Party (NCP), repeated the government position that Sudan wanted to make peace but security issues had to be treated as priority.
"President Bashir told President Mbeki that Sudan was committed to long lasting peace with South Sudan," he told reporters after the meeting. He did not say when talks might resume.
Khartoum accuses Juba of supporting rebels in Sudan's border states of South Kordofan and Blue Nile, charges denied by South Sudan.
(Reporting By Pascal Fletcher in Juba; additional reporting by Ulf Laessing in Khartoum; Editing by Robin Pomeroy)