Libya's United Nations-recognised government launched a military operation on Tuesday to seize a key airbase near the capital Tripoli from renegade General Khalifa Haftar, whose forces have blockaded all key oil terminals.

Libya is the biggest oil producer in North Africa and a key gas exporter to Europe.

Heavy fighting was continuing for control of the Al-Watiya airbase south-west of Tripoli, government sources said.

Al-Watiya is regarded as a key airbase since it is second only to Mitiga International Airport.