Updated June 13, 2019: On Thursday, apparent attacks on two oil tankers in the Gulf of Oman raised alarms about the security of a key petroleum passageway.

Across the Arabian peninsula, thousands of miles of pipes run above and below the desert in one of the world’s most sophisticated production lines for pumping oil from the ground and distributing it around the world. This vast system of oil fields, refineries and ports has largely run like clockwork despite political turbulence across the region.

Then a drone strike claimed by Houthi rebels on May 14 forced the Saudis to temporarily halt the flow of a crucial oil artery to the western side of the country. The assault came a day after mysterious incidents damaged two Saudi tankers and two other ships in a key port in the United Arab Emirates.

These were perhaps the most serious attacks on the kingdom’s oil infrastructure since Al Qaeda militants were thwarted trying to blow up a key Saudi facility at Abqaiq in 2006.