SANAA: Yemen's Houthis issued a new threat to Saudi Arabia's airspace on Sunday after an attack on the kingdom's international airport in Riyadh killed 12 people and wounded hundreds, forcing authorities to stop operations.

Saturday's attack, the deadliest on Saudi soil in more than a decade, was a sharp escalation in the Yemen war, where Riyadh backs the internationally recognised government against the Houthis, who captured swathes of Red Sea coastline in a lightning offensive last month.

While the Iran-backed Houthis stopped short of claiming the strike, they threatened new attacks on the kingdom's airports, except for the holy cities of Makkah and Madinah, warning passengers not to travel.