Saudi state oil company Saudi Aramco halved its oil production on Saturday, after drones had attacked two of the company’s major oil installations. Sources around Saudi Aramco said that production has been reduced by around 5 million barrels per day.

Oil installations in Abqaiq and Khurais were hit by ten drones on Saturday. It was the biggest attack on the oil infrastructure of Saudi Arabia during the current conflict in Yemen. Abqaiq’s oil field in the northeast of the country is home to the world’s largest oil refinery. The field in Khurais, between the capital Riyadh and the Persian Gulf, is one of the most important oil fields in the country. According to a source in Saudi Aramco, the company can probably quickly increase the production of oil again.

Houthi rebels from Yemen have claimed responsibility for attacks on the two Saudi oil installations. The rebel movement has held a large part of Yemen for years, including the capital Sanaa. A coalition led by Saudi Arabia is trying to expel them. Tens of thousands of people have died in the war.