Yemen’s Houthis said they attacked “sensitive” sites in the Saudi capital with missiles and drones, hours after flames and a large plume of black smoke were seen rising above Riyadh airport on Saturday.

The Saudi government sent air raid alerts to citizens by phone overnight warning of aerial attacks, marking the first time the government has issued such alerts for Riyadh since fighting with the Iran-backed Houthis escalated in July.

Explosions were heard in Riyadh as firefighters battled to extinguish the flames of a burning fuel tank emblazoned with the logo of the Saudi oil company Aramco near the city’s King Khalid international airport.