More than 20 people died on Saturday in battles between two Libyan armed factions who have been fighting for nearly three weeks for control of the international airport in Tripoli, the government said.

Fighting in the Libyan capital had quietened down on Sunday morning, but a huge plume of black smoke from a burning fuel depot darkened the sky above the city, still on fire from being hit by a rocket the day before.

Most Western governments have evacuated their embassies after clashes erupted in Tripoli and the eastern city of Benghazi, fearing Libya is sliding back into civil war three years after the uprising that ousted Muammar Gaddafi.

"Tripoli's hospitals received 22 bodies and 72 people were wounded," Libya's government said in a statement on Sunday.

"Mediating committees are still trying to stop the violence and return Tripoli to normal. They have faced difficulties because of the stubbornness of the militias attacking the city."

Islamist-leaning brigades allied to the western port town of Misrata are attacking the airport with rockets and artillery to oust rivals from the mountain town of Zintan who have controlled the airport since the fall of Tripoli in 2011.

Misrata and Zintan rebel fighters once battled side by side to topple the country's dictator. But three years on they have refused to disarm and their rivalries have exploded in a violent struggle over who dominates post-Gaddafi Libya.

In Benghazi, an alliance of Islamist fighters and ex-rebels have banded together to battle Libyan armed forces, seizing a special forces military base last week and pushing the army outside of the city.

Libya's government and weak military have been unable to control the armed factions, who are often semi-official forces approved and paid by ministries and who control huge stockpiles of Gaddafi-era weapons, tanks and missiles. – Reuters