At least 28 people have been killed in renewed fighting between two Sudanese ethnic groups.

At least 28 people have been killed in renewed fighting between two Sudanese ethnic groups, tribal sources said on Saturday.

Battles between the Hamar and Maaliya tribes began Thursday in the border region of West Kordofan and East Darfur states, tribal leaders from each side told media outlets.

Over the past two years, as Sudan's economy weakened, inter-communal clashes over resources have intensified in Sudan's Darfur region, a February report by United Nations chief Ban Ki-moon said.

Tribal militias have become involved in those conflicts, he said.

"Fighting might start again at any time," the Maaliya chief said, adding tensions were sparked by the theft of some cattle.

"Local leaders contained the situation but then unknown people came on camels and burned a Maaliya village, killing six, so fighting started again," the Maaliya source said.

In December, the UN said Hamar-Maaliya fighting killed 38 people in West Kordofan, just over the border from East Darfur. A dispute over grazing rights apparently sparked the clashes.

Fighting between the tribes erupted again in March and April in North and East Darfur, leading people to flee their homes into West Kordofan, the UN's Office for the Coordination of Humanitarian Affairs said on Thursday.