Sudan has continued its bombing of South Sudan, as South Sudan’s president said the attacks amounted to a declaration of war.

Fighting has spread further along the Sudan-South Sudan border with 22 troops killed in a clash between soldiers from both countries.

African Union mediator Thabo Mbeki urged the UN Security Council to take action to stop the fighting between Sudan and South Sudan, warning that both sides are locked in a "logic of war" with hardliners increasingly in control.

Sudanese planes bombarded a disputed oil town near South Sudan's border, a southern military official said, and a doctor said bombs aimed at strategic sites in the south's Unity State killed five people.

South Sudan's president has today vowed that the nation will not withdraw its troops that this week entered a disputed border region with Sudan.