What to know

• Saudi authorities issued their first air raid alert in the capital since fighting returned to neighbouring Yemen, leaving residents of Riyadh rattled after they heard explosions ringing out in the early hours of Saturday. Yemen's Houthis have staged a lightnin...S1
• Yemen's Houthis have staged a lightning offensive this month, seizing swathes of territory in one of the world's poorest countries, leaving the internationally recognised government, which is backed by Saudi Arabia, scrambling to respond.S2