Drones attacked the world’s largest oil processing facility in Saudi Arabia and a major oilfield operated by Saudi Aramco early Saturday, the kingdom’s Interior Ministry said, sparking a huge fire at a processor crucial to global energy supplies, AP reported.

No one immediately claimed responsibility for the attacks in Buqyaq and the Khurais oil field, though Yemen’s Houthi rebels previously launched drone assaults deep inside of the kingdom, and therefore suspicion immediately fell on them.

The fires began after the sites were “targeted by drones,” the Interior Ministry said in a statement carried by the state-run Saudi Press Agency. It said an investigation into the attack was underway.