Oil output from Saudi Arabia plummeted to the lowest level in more than three decades last month due to attacks by Yemen's Houthi militants on its energy infrastructure, according to the International Energy Agency.

The kingdom's oil production fell to just 6 million barrels a day, the Paris-based energy watchdog said, compared with more than 10 million barrels before the Iran war started. In normal times Saudi Arabia vies with Russia to be the second-largest crude producer behind the U.S.

According to the country's own numbers, reported to the oil cartel OPEC, it produced 6.24 million barrels a day in August, the lowest monthly figure so far this year.

Iran-aligned Houthi militants have struck Saudi oil tankers and storage facilities and left a major refinery aflame and offline. At the end of July, they announced a blockade of Saudi ships in the Red Sea, threatening the kingdom's route to market after the effective closure of the Strait of Hormuz. This week, the Houthis captured the port city of Mokha on Yemen's west coast.