An armed group attacked Libya's largest oilfield on Monday, but was repelled after clashes with its protection force, while fighting escalated in eastern commander Khalifa Haftar's effort to capture the capital Tripoli.

The state oil company National Oil Corporation (NOC) said unknown gunmen fired a rocket-propelled grenade at a control station of the El Sharara oilfield. Guards at the site eventually repelled the attackers, an oil engineer there told Reuters.

There were no casualties among oil workers and production was unaffected, the NOC said in a statement.

OPEC member Libya's oil output has been repeatedly disrupted by factional conflict and blockades since the 2011 uprising that ousted Muammar Gaddafi.

Haftar's three-week-old offensive to seize Tripoli, currently occupied by interim government led by Fayez al-Sarraj, has sharpened a power struggle that has fractured Libya since Gaddafi's fall.

The assault by the Haftar-led Libyan National Army (LNA), which is allied to a parallel government based in the eastern city of Benghazi, stalled on Tripoli's stoutly defended southern outskirts last week.

But fighting intensified again on Monday, with both sides using artillery. Shelling was heard in the center of Tripoli coming from southern districts from morning until late at night, residents said.

The Tripoli forces as well as the LNA claimed to have made progress on different parts of the frontline though the situation remained fluid.

A prominent commander from Misrata, a western city allied to Tripoli, has died, the LNA and some websites affiliated with armed groups in Misrata said.

No official confirmation was immediately available.

The battle for Tripoli has killed at least 345 people, including 22 civilians, a World Health Organization official said on Monday. A hospital in Tripoli was evacuated after shelling shattered some windows, the official tweeted.

The United Nations' refugee agency UNHCR said 146 refugees, mainly Africans and a handful of Syrians, were evacuated on Monday from Libya to Italy, where their asylum claims will be processed. Most of them had been transferred earlier this month from detention centers near the fighting, a spokesperson said.

But 3,300 migrants and refugees remain trapped in detention centers near the Tripoli clashes, the UNHCR said.

(Cover: Libyan National Army (LNA) members head out of Benghazi to reinforce troops advancing towards Tripoli, in Benghazi, April 7, 2019. /Reuters Photo)