WorldWhat we know about Houthi attacks on Saudi airports

Saudi Arabia’s energy minister has threatened a “serious” response after deadly Houthi attacks on Riyadh’s international airport. Flights remain suspended and are expected to stay grounded for days. The Houthis say the attacks retaliate for what they call “brutal Saudi aggression” in areas they control in western Yemen. BBC security correspondent Frank Gardner examines why Saudi Arabia has been unable to stop them.