Yemen's Iran-aligned Houthi group has claimed responsibility for the drone attacks on Saudi Arabian oil facilities, which occurred at around 4AM Saturday local time.
Saudi Arabia's state-run oil company Saudi Aramco says the strikes will cut the kingdom's oil output by 5.7 million barrels a day, which is about half Saudi Arabia's total output and more than 5 percent of global oil supply.
The incident is causing concerns over a possible hike in global oil prices.
Aramco will temporarily close the facilities while it fixes the damage, but its Chief Executive said no casualties were reported from the attacks.
Abqaiq, one of the sites targeted in the attacks, is the largest oil processing plant in Saudi Arabia,while the other target, Khurais, is in the country's second largest oilfield.
The incident comes as Aramco is seeking to go public in what could well be the world's biggest initial public offering.
U.S. Secretary of State Mike Pompeo has claimed Iran is behind the strikes. Through Twitter, he called the strike on the world's energy supply "unprecedented" and argued there is "no evidence the attacks came from Yemen."
Washington condemned the attacks and President Trump told Crown Prince Mohammed bin Salman that the U.S. was ready to work with Saudi Arabia for its security.
The U.S. energy department said it would work with the International Energy Agency, if necessary, to deal with the incident.
Yoon Jung-min, Arirang News.