Saudi Arabia’s crude exports fell last month to their lowest level in at least nine years, as attacks on tankers intensified amid escalating tensions in West Asia.

Tanker-tracking data compiled by Bloomberg, Vortexa and Kpler showed that Saudi oil exports averaged around 3 million barrels per day in August, the lowest level in records dating back to early 2017. The figure is consistent with estimates from crude traders and a person familiar with Saudi oil operations.

This week, two more tankers carrying Saudi crude were struck by projectiles in the strait. One of the vessels belonged to Saudi shipping company Bahri, which reported that two crew members were killed.

The attacks have made some Saudi customers increasingly hesitant to use the kingdom’s Red Sea ports, forcing Riyadh to consider alternative routes around Africa. Such voyages add thousands of kilometers to shipping routes and further disrupt global supply chains.

Tracking data showed exports through the western port of Yanbu rose to around 4.3 million barrels per day (bpd) in June, from approximately 770,000 bpd in January. Yanbu exports then declined to about 3.7 million bpd in July after Ansarallah announced a blockade on Saudi shipping, before falling further to roughly 2.25 million bpd in August. Meanwhile, shipments through the Persian Gulf, which had recovered slightly to around 800,000 bpd in July, declined again the following month.