Three Libyan tribesman have been killed in fighting that grew out of disputes between army units under conflicting orders over who controls key resources in the country's east, officials said Monday.

Another five people were wounded in the fighting between Toubou and Zuwayya tribesmen on Sunday night in Ajdabiya, 160 kilometres (100 miles) south of Benghazi.

The clashes were sparked by fighting on Friday between one unit made up of Zuwayya, under the orders of the general staff, and a Toubou unit that takes its orders directly from the defence ministry, an official explained.

At stake was control over oil wells and an agricultural water reservoir in Al-Sarir, 600 kilometres south of Benghazi, he added.

Five soldiers were killed in the fighting on Friday, and clashes broke out between Zuwayya and Toubou in Ajdabiya the following day after the soldiers' burial that spilled over into Sunday.

The Zuwayya, who are Arab, and the Toubou, who are black, have a long history of conflict.

Following the overthrow of long-time dictator Muammar Gaddafi in 2011, tribal unrest broke out in parts of Libya, particularly in the south and west, prompted by a settling of grudges or competition for control of smuggling across the country's borders.

Since Gaddafi ouster, Libya's authorities have struggled to impose their authority and stem rising lawlessness.