The two tribes fight frequently over land and cattle.

The United Nations says it is worried about tension in Jonglei, one of the worst-hit states for ethnic violence in South Sudan.

The Security Council said in Monday's statement it welcomed efforts by the South Sudanese government to mediate a solution to the conflict.

It also said the council is concerned over the sophistication of weapons used in the recent conflicts, and encouraged the U.N. mission to continue to support efforts to disarm, demobilize, and reintegrate former rebel fighters.