Strikes by Yemen's Houthis on Sunday killed at least 11 people, a medical source in the Yemeni port city of Mokha has told AFP, after an earlier drone salvo targeted a Saudi oil refinery on the Red Sea coast.

A years-long truce in Yemen's civil war between the Houthis and the Saudi-backed internationally recognised government appeared to collapse last month.

It came as the Houthis announced a maritime blockade of Saudi Arabia, hitting Saudi tankers in the Red Sea and the kingdom's oil infrastructure, in parallel with Iran's blockade of the Strait of Hormuz.

A medical source in Mokha, held by Yemen's internationally recognised, Aden-based government, said three civilians and eight military personnel had been killed in the Houthi attacks.

A further 32 individuals were wounded, six of them civilians, the source added, explaining all the civilian casualties had been a result of strikes on Mokha's port.

The Houthis' military spokesman Yahya Saree said the group had targeted "Saudi enemy" troops and equipment in the area with missiles and drones.

Earlier, Saree said the Houthis had struck an oil facility on Saudi Arabia's Red Sea coast after the Gulf kingdom's energy ministry said it had extinguished a fire at the Jazan site.

He added that the attack on the facility operated by Saudi Arabia's state-owned oil firm Aramco was launched in response to incursions by drones from the Gulf monarchy into northwest Yemen.