Updated

MALAKAL, Sudan -- North Sudan's military has bombed a disputed north-south border area, a U.N. official said Saturday, but a Southern Sudan army spokesman said the bombing was not a provocation.

Col. Philip Aguer, spokesman for the Sudan People's Liberation Army which protects Southern Sudan, said the air attack, which occurred on Friday, hit the south region by mistake.

Aguer said north Sudan military officers consulted with their southern counterparts through a joint military panel after the bombing and determined the bombs were launched in the north, but landed in Southern Sudan territory close by. The panel, called the Joint Defense Board, is part of the 2005 peace deal and is meant to help avoid misunderstandings between the armies of the north and the south.

"The bomb fell in our territory by mistake and the SAF (Sudan Armed Forces) admitted it was not intentional," said Aguer. He said the bombing took place in Northern Bahr Gazal State, located in the southwest of the country and part of Southern Sudan, but would not give a precise location.

Chiefs of staff from both armies spoke by telephone early Saturday, after the incident, Aguer said. He said there were casualties but declined to give details.

Aguer said that north Sudan's airforce possibly could have been targeting members of the Justice and Equality Movement rebel group, which has bases in Southern Darfur state bordering Northern Bahr Gazal. JEM is the most powerful of the Darfur rebel groups and has been fighting a rebellion in western Sudan's since 2003.

Several other rebel groups in the region have signed peace deals with the Sudanese government, but JEM remains one of the holdout groups.

The top U.N. official in Southern Sudan, David Gressly, said Friday's bombing took place in the "Kiir River valley" in southwestern Sudan. Gressly said the casualties are in the single digits and a U.N. team is going to the area to assess the situation.

The borders of Northern Bahr Gazal and Southern Darfur are in dispute. Under a 2005 peace deal the border between Southern Sudan and the north is supposed to be demarcated. That exercise, however, has been fraught with delays.

The same peace deal also requires Southern Sudan holds an independence referendum in January to determine if they will remain a part of Sudan. There has been a lot of back and forth over whether that vote will be delayed, raising tensions and concerns there could be renewed conflict.

Southerners fought a two-decade civil war against the Muslim, northern-dominated central government in which 2 million people died and more than a million headed north to escape the fighting. The independence referendum will be the culmination of the six-year transitional period that was part of the 2005 peace deal that ended that 20-year north-south conflict.