Yemen's Houthis have urged "international shipping companies," civilians and workers to evacuate Saudi airports and oil facilities, vowing on Oct. 14 to press on with attacks a day after a strike that sources said caused extensive damage to Saudi Aramco's headquarters in Dhahran.

The call goes to the heart of Gulf logistics. The Dhahran complex hosts a major operations center for Aramco, which oversees a vast network of onshore and offshore oil rigs, pipelines, refineries and export terminals. Operations at Aramco were continuing normally, with employees working from home, according to two people with knowledge of the matter. Aramco did not immediately reply to a request for comment.

Tuesday night's attack caused a fire that spread across several floors of the Aramco base, three sources told Reuters. The Saudi energy ministry had described the fire as limited.

What has been hit so far?

The Houthis said Wednesday they had launched ballistic missiles, cruise missiles and drones at Aramco facilities in Dhahran, Riyadh's King Khalid International Airport, and an Aramco refinery in Riyadh. Riyadh's international airport has now come under attack four times.

The Saudi-led coalition said it intercepted a ballistic missile fired toward Riyadh on Wednesday. Several loud booms were heard in the Saudi capital after authorities issued, then lifted, an aerial threat alert.

Saturday's strike on King Khalid International killed 13 people — the deadliest attack in Saudi Arabia in a decade. Authorities have closed the airport until Oct. 17, and airlines have canceled flights to the kingdom.

Why does the Bab el-Mandeb Strait matter here?

The conflict restart is entangled with Red Sea geography. Saudi Arabia resumed its military campaign in Yemen last month to reverse sudden Houthi gains, after the fighters swept down the Red Sea coast to the critical Bab el-Mandeb Strait — the chokepoint at the southern mouth of the Red Sea and a main artery for Asia–Europe container and tanker traffic.

Saudi Arabia intervened in Yemen's civil war in 2015 after the Houthis seized the capital Sanaa, fearing Iranian influence and chaos on its borders. A UN-brokered 2022 truce held a fragile peace until this year. The Houthis frame their attacks as retaliation for Saudi strikes on Yemen and for Riyadh's backing of Yemeni government forces.

The escalation has dealt a blow to Crown Prince Mohammed bin Salman's plans to transform and diversify the Saudi economy and reduce reliance on oil.

What is the humanitarian fallout?

The Red Cross said Wednesday that hospitals across Yemen are struggling to cope with a sharp rise in war casualties as fighting intensified along multiple front lines. The UN World Food Programme said assistance had been cut off to the government-held city of Taiz, encircled by Houthi fighters earlier this month.

"WFP and its partners cannot access more than 600,000 people in Taiz who depend on humanitarian assistance, including more than 200,000 women and children," the agency said in a statement.

With the Houthis declaring Saudi airports and oil infrastructure legitimate targets and renewing their grip on the Bab el-Mandeb approach, carriers, airlines and fuel suppliers face the prospect of a wider, longer disruption to Gulf routes.