• A spokesman for the Iran-aligned Houthi group in Yemen said it had deployed 10 drones in the attacks.
• Saudi officials have not yet commented on who could be behind the attacks.
Drone attacks have set alight two major oil facilities run by the state-owned company Aramco in Saudi Arabia, state media say.
Footage showed a huge blaze at Abqaiq, site of Aramco's largest oil processing plant, while a second drone attack started fires in the Khurais oilfield.
The fires are now under control at both facilities, state media said.
A spokesman for the Iran-aligned Houthi group in Yemen said it had deployed 10 drones in the attacks.
The military spokesman told al-Masirah TV, owned by the Houthi movement and based in Beirut, that further attacks could be expected in the future.
Saudi officials have not yet commented on who could be behind the attacks.
"At 04:00 (01:00 GMT), the industrial security teams of Aramco started dealing with fires at two of its facilities in Abqaiq and Khurais as a result of... drones," the official Saudi Press Agency reported.
"The two fires have been controlled."
What are the facilities?
The Abqaiq plant turns sour crude into sweet crude, producing up to 7 million barrels a day. Aramco says it is the world's largest "crude oil stabilisation plant".
Saudi security forces foiled an attempt by al-Qaeda to attack the Abqaiq facility with suicide bombers in 2006.
The Khurais oilfield came on line in 2009 and is the nation's second-largest after Ghawar. Khurais reportedly produces 1.5 million barrels a day with estimated recoverable oil reserves of more than 20 billion barrels.
Global oil markets are closed for the weekend so there was no immediate effect on prices.
The attacks come as Aramco prepares for a much-anticipated initial public offering (IPO), part of a reform package led by King Salman's son, Crown Prince Mohammed bin Salman, to reduce the economy's reliance on oil.
Who carried out the attacks?
The Iran-aligned Houthi rebel movement has been fighting the Yemeni government and a Saudi-led coalition.
Yemen has been at war since 2015, when President Abdrabbuh Mansour Hadi was forced to flee the capital Sanaa by the Houthis. Saudi Arabia backs President Hadi, and has led a coalition of regional countries against the rebels.
The coalition launches air strikes almost every day, while the Houthis often fire missiles into Saudi Arabia.
The Houthi military spokesman told al-Masirah that operations against Saudi targets would expand "as long as its aggression continues".
Houthi fighters were blamed for drone attacks on the Shaybah natural gas liquefaction facility last month and on other oil facilities in May.
There have been other sources of tension in the region, often stemming from the rivalry between Saudi Arabia and Iran.
Saudi Arabia and the US both blamed Iran for attacks in the Gulf on two oil tankers in June and July, allegations Tehran denied.
In May, four tankers, two of them Saudi-flagged, were damaged by explosions within the UAE's territorial waters in the Gulf of Oman.
Saudi Arabia and then US National Security Adviser John Bolton blamed Iran. Tehran said the accusations were "ridiculous".
Tension in the vital shipping lanes worsened when Iran shot down a US surveillance drone over the Strait of Hormuz in June, leading a month later to the Pentagon announcing the deployment of US troops to Saudi Arabia.