A health official in Libya says 15 people have been killed in clashes between two tribes in the country's south.

The fighting is pitting the al-Tabw tribe against the Awlad Soliman tribe in the city of Sabha. A local leader said Saturday that the fighting was sparked by the killing of a guard of the city's military leader, a member of the Awlad Soliman tribe.

The health official confirmed the casualty figure and spoke on condition of anonymity as he was not allowed to brief journalists.

For more than two years, Libya has been held hostage by increasingly powerful militias, initially formed from the rebel brigades that fought against dictator Moammar Gadhafi in the country's 2011 civil war.