The worst fighting in Libya's capital for years calmed on Wednesday an hour after the government announced a ceasefire, Tripoli residents said, with no immediate statement from authorities on how many people had been killed.

Clashes broke out late on Monday after the killing of a major militia leader. After calming on Tuesday morning, the fighting reignited overnight, with major battles rocking districts across the entire city.

"Regular forces, in coordination with the relevant security authorities, have begun taking the necessary measures to ensure calm, including the deployment of neutral units," the government's defence ministry said.

The ministry said the neutral units it was deploying around sensitive sites were from the police force, which does not carry heavy weapons.

The United Nations Libya mission UNSMIL said it was "deeply alarmed by the escalating violence in densely populated neighbourhoods of Tripoli" and urgently called for a ceasefire.

Monday's clashes had appeared to consolidate the power of Abdulhamid al-Dbeibah, prime minister of the divided country's Government of National Unity (GNU) and an ally of Turkey.

However, any prolonged fighting within Tripoli risks drawing in factions from outside the capital, potentially leading to a wider escalation between Libya's many armed players after years of relative calm.

The main fighting on Wednesday was between the Dbeibah-aligned 444 Brigade and the Special Deterrence Force (Rada), the last major armed Tripoli faction not currently in his camp, the English-language Libyan Observer reported.

Fighting also erupted in western areas of Tripoli that have historically been a gateway for armed factions from Zawiya, a town to the west of the capital.

WEEKS OF GROWING TENSIONS

Tripoli residents trapped in their homes by the fighting voiced horror at the sudden eruption of violence, which had followed weeks of growing tensions among armed factions.

"It's terrorizing to witness all this intense fighting. I had my family in one room to avoid random shelling," said a father of three in the Dahra area by phone.

In the western suburb of Saraj, Mohanad Juma said fighting would pause for a few minutes before resuming. "Each time it stops we feel relieved. But then we lose hope again," he said.

Libya has had little stability since a 2011 NATO-backed uprising ousted longtime autocrat Muammar Gaddafi and the country split in 2014 between rival eastern and western factions, though an outbreak of major warfare paused with a truce in 2020.

A major energy exporter, Libya is also an important way station for migrants heading to Europe and its conflict has drawn in foreign powers including Turkey, Russia, Egypt and the United Arab Emirates. Its main oil facilities are located in southern and eastern Libya, far from the current fighting in Tripoli.

While eastern Libya has been dominated for a decade by commander Khalifa Haftar and his Libyan National Army (LNA), control in Tripoli and western Libya has been splintered among numerous armed factions.

Dbeibah on Tuesday ordered the dismantling of what he called irregular armed groups.

That announcement followed Monday's killing of major militia chief Abdulghani Kikli, widely known as Ghaniwa, and the sudden defeat of his Stabilisation Support Apparatus (SSA) group by factions aligned with Dbeibah.

The seizure of SSA territory in Libya by the Dbeibah-allied factions, the 444 and 111 Brigades, indicated a major concentration of power in the fragmented capital, leaving Rada as the last big faction not closely tied to the prime minister.