The Saudi-led coalition on Saturday launched a "large-scale" assault on Yemen after a projectile killed two people in the kingdom, in the first such deaths in three years blamed on Iran-backed Huthi rebels.

A retaliatory coalition air strike on Yemen killed three people and wounded six others in Ajama, a town northwest of the Huthi held capital Sanaa, Yemeni medics said.

Yemen has been wracked by civil war since 2014 pitting the internationally recognised government supported by the Saudi-led military coalition against the Huthis who control much of the north.

Tens of thousands of people have since been killed, in what the UN has described as the world's worst humanitarian crisis.

Saudi's civil defence said that two people, one Saudi and the other Yemeni, were killed and seven others wounded in the projectile attack on Jazan, a southern region of the kingdom bordering Yemen.

"A military projectile fell on a commercial store on the main street, resulting in two deaths," it said in a statement, adding six Saudis and a Bangladeshi national were wounded.

The Saudi-led military coalition said shortly afterwards that it was "preparing for a large-scale military operation".

It responded later with an air strike in which "three civilians including a child and a woman were killed, and six others were wounded", the Yemeni medics told AFP.

The coalition said it would hold a news conference later on Saturday to address the latest developments.

Yemen's Huthis regularly launch missiles and drones into neighbouring Saudi Arabia, targeting its airports and oil infrastructure.

But the latest was the first in more than three years that has resulted in fatalities in the kingdom, which recorded its first death from a Huthi missile attack when a missile struck Riyadh in 2018.

It also comes as fighting between the two sides intensifies, with the coalition ramping air strikes on Sanaa.