Three days of clashes in southern Libya that have killed dozens of people have spread to Sabha, the country’s fourth largest city.
Hundreds of government soldiers have been sent to try to calm the situation.
Gunmen from Sabha are fighting others from the Tibu ethnic group.
Hampered by no coherent army, the ruling National Transitional Council is struggling to assert its authority across Libya.
Rival militias and tribal groups are competing for power and resources after the revolution that ousted Muammar Gaddafi.
Last month government forces did manage to contain tribal clashes in the southeast.