It's expecting more than a million people to flee the country as fighting rages between the army and rival militia forces.

The UN's humanitarian affairs co-ordinator, Ramesh Rajasingham, said more than half Sudan's population - 25 million people - needed aid and protection.

He says it's the highest number ever seen in the country.

Access for aid agencies remains a huge challenge.

Supplies have been looted and aid workers attacked since the conflict erupted a month ago.