ADEN - Houthi forces fired mortar rounds at an oil refinery in the southern Yemeni city of Aden on Monday, starting a huge fire, witnesses and local officials said.

The mortar barrage hit three full storage tanks, in an incident sure to add to the fuel crisis in the southern port.

After months of conflict, most of Yemen's oil and gas industry has ground to a halt.

The attack on the refinery in the Buraiqah area sent black smoke and flames swirling high into the night sky.

"We are trying to put out the fire. The shelling targeted the tanks where we were storing diesel and fuel for local consumption in Aden. The damage is going to be very big," one official at the facility told Reuters on condition of anonymity.

The Houthis, who took over the capital Sanaa last September, have been battling local fighters in the south for three months and had attacked the refinery before.

An Arab coalition led by Saudi Arabia has been bombing the Houthis for three months to try to restore Yemen's exiled government, and has imposed a near-blockade on the country, cutting off trade in food and fuel.

Industry sources said in April the 150,000 barrels-per-day Aden refinery had shut its operations and declared force majeure on its imports and exports due to the war.

Residents say that despite heavy shelling, locals had been able to tap the refinery's oil and gas supplies to meet their own needs.

Nationwide fuel shortages have spread disease and suffering in a country where access to water usually depends on fuel powered pumps and over 20 million people - 80 percent of the population - need aid, according to the United Nations.

More than 3,000 people have been killed and over a million displaced in the conflict, which pits the Arab coalition against the Iranian-allied Houthis.

A week-long UN-brokered ceasefire was meant to begin on Saturday to allow the delivery of aid.

It failed to take hold, after Saudi Arabia refused to recognise the truce and continued air strikes.

Reuters