Valerie Amos, UN senior official, urged Sudan to lift a ban on international UN staff travelling to border states [Reuters]

The United Nations has received alarming reports of malnutrition in two Sudanese border states where the army is fighting armed groups, a senior UN official has said.

Fighting broke out in June between the Sudanese army and Sudan People's Liberation Movement-North rebels in South Kordofan and spread in September to the state of Blue Nile. Both states border newly independent South Sudan.

"I received alarming reports with respect to malnutrition and the food situation, particular in areas that are controlled by SPLM-North," Valerie Amos, UN Under-Secretary General for Humanitarian Affairs, told reporters in Khartoum on Wednesday.

She urged Sudan to lift a ban on international UN staff travelling to both border states.

Since the outbreak of fighting, UN agencies and aid groups have only been able to keep small teams of local staff on the ground and the government has stopped any aid workers visiting areas where there has been fighting.

"We need to ensure that the UN capacity, which is there to support government efforts, is made up of a mix of  UN staff, national and international, to make sure we have the right skill set of support," Amos said after talks with Sudanese officials.

Amira Fadhil, the social and welfare minister, told journalists the ban was there to protect foreign workers and would stay in place.

"We fear for the security of foreigners. That's why we think the presence of a Sudanese organisation makes sense. But we want to grant access as soon as possible," she said.

The violence has already forced about 417,000 people to flee their homes, more than 80,000 of them to South Sudan, the United Nations estimates. Locals have faced air raids and sporadic ground fighting, according to rights groups and refugees.

South Sudan declared independence in July, under the terms of a 2005 peace deal that ended decades of civil war with the Khartoum government.

Both Blue Nile and South Kordofan contain groups who sided with the south in the civil war and say they continue to face persecution inside Sudan.

SPLM-North is one of  a groups of rebel movements in underdeveloped border areas who say they are fighting to overthrow Sudan's President Omar Hassan al-Bashir and end what they see as the dominance of the Khartoum political elite.