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Two major assets owned by Saudi Arabia’s national oil company were attacked overnight on Friday, forcing the world’s No. 2 oil producer to shut in half of its daily production.

Media reports said up to 10 drones were used to attack the Abqiaq oil processing plant in Saudi Arabia’s eastern province and the Hijra Khurais oil field. Iranian-backed militants fighting against Saudi Arabia in Yemen took credit for the weekend attacks.

The Abqaiq plants stabilizes and removes sulfur from crude oil so it can be exported safely. A statement from Saudi Arabia’s Ministry of the Interior said a fire at the plant had been contained. But there is no word on the extent of the damage.

The Abqiaq plant was a previous target for militants in 2006, when a bomb exploded outside the plant. The Abqiaq plant is capable of producing up to 7 million barrels per day of oil.

Saudi Arabia oil assets. (Source: Energy Information Administration)

The Hijra Khurais field produces another 1.5 million barrels per day of oil. Saudi Arabia produces 12 million barrels per day of oil.

Saudi Aramco is said to be looking at tapping its oil reserves to meet customer commitments.