Rival militias clash in Tripoli, highlighting Libya's fragility

Clashes between rival militias in Tripoli result in at least 45 deaths
Senior commander of the 444 brigade held by rival group, later released
Libyan prime minister Abdul Hamid Dbeibah warns against further militia fighting and threatens "other measures"
The fighting highlights the divided state of Libya between rival administrations and control by well-armed militias
Dbeibah warns militias against escalating clashes that could lead to more deaths