29 December 2011 Last updated at 17:40 GMT
Seventeen South Sudanese civilians have been killed during air raids by Sudan’s military, an official has told the BBC.
South Sudan’s military spokesman Philip Aguer said those killed were cattle herders in West Bahr al-Ghazal state – further west than other recent clashes.
Sudan has denied the allegations but Col Aguer said no other power in the region could carry out the bombing.
The south seceded from Sudan in July but there have been numerous clashes along their common border.
“This is a hostile aggression that Khartoum has been conducting against the civilian population,” Col Aguer told the BBC’s Focus on Africa programme.
Most other clashes have been in the south’s Unity state and South Kordofan and Blue Nile in the north.