The move came after a drone strike sparked a fire at a Riyadh oil refinery Friday, in an attack claimed by the Huthis, as the Iran-backed rebels made major advances on Marib, seizing a strategic mountain.

The official Saudi Press Agency published footage of air strikes launched by the coalition, saying the campaign was designed to "thwart the Huthi militia's attempt to advance towards Marib in Al-Kasrah".

Al-Kasrah is one of the lines of defence to the northwest of the city, which is the government's last remaining stronghold in the north and the capital of an oil-rich region.

The coalition, which entered the Yemen conflict in 2015 to defend the beleaguered government, said it had succeeded in destroying Huthi military equipment, including tanks, and inflicting "heavy losses".

Rebel-controlled Al-Masirah television reported 38 air strikes across various parts of Marib, while a government official told AFP that the coalition had launched at least 20 strikes.

"At least 70 fighters were killed, including 22 from the government forces, and dozens were injured in clashes in the past 48 hours," the source told AFP.

"The rebels launched a violent attack, including with tanks, in al-Kasrah and the attack was thwarted with aerial support from the coalition."

The Huthis and the internationally recognised government have been locked in a power struggle since 2014, when the rebels overran the capital Sanaa. Since last month, the rebels have been pushing to seize Marib.

Loss of the city would be a huge blow for the Yemeni government, but would also threaten catastrophe for civilians, including at least one million displaced people sheltering in the region, many in desolate camps in the surrounding desert.

Despite the latest rebel advance, analysts say the city may not fall any time soon, given the coalition's overwhelming firepower.