On the frontline of the conflict between Sudan and South Sudan

Sudan has reportedly declared a state of emergency along its border with South Sudan after weeks of clashes.

The decree will apply in the border districts of the South Kordofan, White Nile and Sennar states, according to the state-run Suna news agency.

On Saturday, four people, including a British and a South African man were arrested in the oil-rich area of Heglig, accused by Sudan, of carrying out 'suspicious work.'

But the UN mission in South Sudan says the four were aid workers, involved in mine clearance work.

Africa Correspondent, Andrew Harding, reports from South Sudan.