Yemen's Iran-aligned Houthis announced they had struck Riyadh airport with a ballistic missile, an impressive feat of marksmanship that they declined to substantiate with any actual evidence. Saudi Arabia, for its part, offered the diplomatic equivalent of a shrug and did not immediately comment.

Three people briefed on the matter, however, told Reuters that shrapnel from an interception - or possibly another projectile entirely - left a Saudia Airlines commercial plane heavily damaged after it caught fire while parked at a terminal on Thursday. No passengers were believed to have been aboard at the time, though officials couldn't rule out injuries, because certainty is apparently too much to ask.

Witnesses reported hearing explosions in Riyadh, including a large blast at King Khalid international airport. One witness told the Associated Press that fire and ambulance crews were deployed, while a video verified by Reuters showed a thick black column of smoke and flames rising from the airport. The witness, speaking on condition of anonymity, said outgoing flights were halted and passengers were told to evacuate - presumably with the standard airline efficiency of everyone calmly forming a single-file line.

Lufthansa and Air India confirmed they were suspending flights to Riyadh. According to data compiled by aviation analytics company Cirium, almost half of departures from the airport had been cancelled by 1500 GMT on Thursday, with 31 more cancellations expected for Friday across all Saudi airports. Nothing says "business as usual" like a 50% cancellation rate.

This comes after Saudi authorities said on Wednesday that three people had been killed this week in strikes on Riyadh airport and Abha airport in the country's southwest. The Houthis escalated their campaign on Thursday, attempting to shut down the kingdom's airspace and warning workers to stay away from energy plants, which they promised would be targeted. Saudi officials separately said debris from an intercepted missile had hit a kindergarten and medical complex in Riyadh - because nothing says "precision strike" like a kindergarten.

The Houthis say they are targeting the kingdom over its support for government forces in Yemen's reignited civil war. Saudi Arabia says it is backing an offensive by Yemen's UN-recognised government to take back territory from the Houthis. The Houthis have made a lightning advance across Yemen's coastal plain over the last month, appearing to gain ground in the country's south-west on Wednesday as the group approached the city of Taiz.

Independent observers said earlier this week there was danger the group was on course to capture Taiz, with some signs that forces linked to the Saudi-backed government were pulling back to secure the major port city of Aden. Riyadh is due to host a major meeting of energy policymakers, the WPC Energy Congress, this week - because what better time to discuss oil policy than when missiles are flying at your airport?