Sudanese warplanes have bombed South Sudan, wounding six civilians in areas bordering war zone regions where Khartoum is trying to crush rebel fighters, reports said Friday.

Sudan however rejected the claims of fresh bombing raids, which not only raises tensions between the former civil war foes, but also comes as Khartoum holds peace talks with rebels.

South Sudan army spokesman Philip Aguer told the independent Radio Tamazuj that bombs were dropped on Wednesday in the Maban district of Upper Nile state, which hosts over 125,000 refugees who fled from fighting in neighbouring Sudan's Blue Nile state.

Sudanese army spokesman Colonel Al-Sawarmy Khaled denied the reports.

"This allegation is completely incorrect and we didn't bomb any area inside South Sudan's territories, and we have no links with such a thing," he told AFP.

Khartoum officials are meeting in Ethiopia with rebels from war-torn Blue Nile and South Kordofan, with African Union mediator Thabo Mbeki calling for an "urgent" ceasefire.

Earlier this month the presidents of Sudan and South Sudan agreed to restart work to demarcate their contested border, a dispute that boiled over into war between the countries in 2012.

South Sudan split from the north in 2011 following a peace agreement ending decades of civil war, and the two remain at odds over unresolved issues from the secession, including the frontier.

Both countries are also battling internal conflicts that spill over their borders.

Civil war broke out in South Sudan in December.

Sudan's army has been fighting for more than a decade war in the western Darfur region, and for the past three years, rebellions in South Kordofan and Blue Nile.

Warplanes earlier this month reportedly also bombed South Sudan's Western Bahr el-Ghazal region, which borders Darfur.

Local officials told the Radio Tamazuj station that 16 people had been wounded in Raja county on November 2 after bombs were dropped by unknown aircraft.