At least 55 people have been killed in the new round of fighting between the rival military factions in the Libyan capital Tripoli.

Armed factions battled in several districts overnight and into Tuesday morning in the city's worst violence this year.

However, the military commander at the center of clashes between rival militias in the Libyan capital has been released.

The detention of Mahmoud Hamza, the commander of the 444 Brigade, had triggered the violence in Tripoli.

He was released on Tuesday evening by the Special Deterrence Force, according to sources cited in a Reuters report. 

The 444 Brigade and the Special Deterrence Force both backed the interim Government of National Accord (GNA) during brief battles last year.

Libya has been beset by violence and chaos since the overthrow and killing of its long-serving ruler Muammar Gaddafi following a bombing campaign by the US-led NATO military alliance in 2011. The resulting chaos and factional divisions then escalated into a regional proxy war fueled by foreign powers, who poured weapons and mercenaries into the country.

Since 2015, Libya has been divided between the internationally-recognized GNA in Tripoli and lawmakers in Tobruk, allied to renegade military commander Khalifa Haftar.

The Government of National Unity of Libya was supported by countries such as Qatar, Turkey, some European countries and the United Nations, and countries such as Egypt, Russia, Saudi Arabia and the UAE also supported the army of Khalifa Haftar, a retired general based in Benghazi and Tobruk.

The two rivals fought for power in the country for several years, and after a year of intense conflict that led to the advances of the government of unity to the capital city of Tripoli, they announced a ceasefire in last August.