The Iran-backed Houthis, who control most of Yemen's populated areas including the capital Sanaa, said they had deployed drones and missiles to strike a Saudi air-base in Khamis Mushait and targeted facilities belonging to state oil giant Saudi Aramco in Abha, Najran and Jazan.
Saudi authorities confirmed 73 people were hurt, among them women and children. NASA satellite images showed a thick cloud of black smoke over the Jazan refinery and a column of white smoke rising from an oil distribution centre in Abha.
The attacks appear to be among the largest carried out against Saudi Arabia since the United States and Israel launched their war against Iran in February, according to reports. The Houthi operation targeted facilities connected to an alternative route to the Strait of Hormuz, the Bab el-Mandeb, a strategic waterway off the southern tip of the Arabian Peninsula.
Houthi spokesperson Yahya Saree accused Riyadh of escalating the war by launching air strikes on Yemen, saying the Houthis would respond. Saudi-led coalition spokesperson Turki al-Malki said the coalition "will take all necessary operational measures to deter this terrorist militia and resolutely confront its hostile approach."
Houthi-controlled media later reported that Saudi war-planes had carried out four air-strikes in Yemen's Jubah district east of Sanaa. The International Organization for Migration said more than 18,500 people had fled their homes because of fighting along Yemen's west coast over the past three days.
The renewed fighting has the potential to worsen the war's global economic impact by disrupting oil supplies. Global oil prices rose in response to the attacks.