The U.S. said cruise missiles might have been involved, and President Trump said the possibility of Iranian involvement was being assessed.

The Houthis have threatened more drone attacks. Iran has denied responsibility.

Impact: Oil prices jumped faster than at any time in over a decade. The attack on Saudi Arabia’s Abqaiq plant, which accounts for 5 percent of global oil supplies, and a nearby facility took 5.7 million barrels a day of production off line for at least a few days.

It also revealed the significant danger drones pose to the Persian Gulf’s sprawling processing plants, pipelines and refineries.