Fighting in Yemen's north has left dozens dead and wounded, a government source said Friday, as Huthi rebels battle to seize a strategic oil-rich region.

Yemen's Iran-backed Huthis have resumed an offensive to seize Marib, the government's last northern stronghold, with reports of heavy clashes with pro-government forces, including air strikes pounding a rebel convoy.

"Dozens of people have been killed and wounded on both sides," a government source told AFP, claiming that "most of the deaths were Huthis hit by air strikes."

The loss of Marib would be disastrous for the beleaguered leadership.

On Thursday night, Huthi fighters fired a missile into the suburbs of Marib "killing eight soldiers and wounding many others," he added.

Military sources said the Saudi-led coalition launched several air strikes on Huthi positions near Marib, including destroying a rebel convoy of eight vehicles, killing all.

Marib lies some 120 kilometres (75 miles) east of the capital Sanaa, which the Huthis have held -- along with much of the north -- since 2014.

Residents in Marib said the city was on alert and that government forces had appealed on local tribes to support them.

This month the rebels launched a new push for Marib, and also escalated attacks against Saudi Arabia, drawing condemnation from the international community.

Yahya Sarie, spokesman for the Huthis' armed wing, claimed responsibility for the most recent attack, with drones and missiles fired Thursday at the southern Saudi garrison town of Khamis Mushait, a key airbase.

That attack was intercepted before it reached its target.

On Wednesday, the rebels mounted a drone attack on Saudi's southwestern Abha airport, leaving a civilian plane ablaze.

The upsurge in violence comes shortly after the United States decided to remove the rebels from its list of terrorist groups, in order to ensure humanitarian work in Yemen is unimpeded, and to pave the way to restart peace talks.

Yemen's grinding conflict has claimed tens of thousands of lives and displaced millions, according to international organisations, sparking what the UN calls the world's worst humanitarian crisis.

On Friday, the UN agencies warned that about 400,000 children aged under five are in danger of dying of acute malnutrition this year.