Saudi Arabia’s oil production and exports have reportedly been cut in half, said three sources familiar with the matter, after drone attacks on two Aramco plants on Saturday, including the world’s biggest oil processing facility.

One of the sources said the attacks have impacted 5 million barrels per day of oil production — almost half the kingdom’s current output. The source did not elaborate.

Saudi Aramco operates the world’s largest oil processing facility and crude oil stabilization plant in the world at Abqaiq, in eastern Saudi Arabia. The plant has a crude oil processing capacity of more than 7 million barrels per day.

Iran-backed Houthi rebels in Yemen, who have launched several drone attacks on Saudi targets, have claimed responsibility.