A loud explosion was heard in Saudi Arabia's capital Riyadh on Tuesday, but the cause was not immediately known. Several witnesses reported hearing two loud bangs and seeing a small plume of smoke above the capital just before 1pm local time (10am GMT). Social media users have shared videos of a ballistic missile interception. There was no immediate comment from Saudi authorities, or any claim of responsibility. Yemen's Iran-backed Houthi rebels have carried out many cross-border attacks on Saudi Arabia using drones and missiles since the Saudi-led coalition intervened in Yemen to support the internationally-recognized government against the Houthi rebels in 2015. Missile attacks and drone strikes claimed by Houthis have targeted cities, airports, and oil infrastructure in the Kingdom, occasionally reaching Riyadh. On Saturday, the Saudi-led oalition said it had intercepted and destroyed an “enemy air target” launched towards Riyadh.