Oil tankers passing through the Strait of Hormuz “must be very careful,” the spokesman for Iran’s Ministry of Foreign Affairs warned on Monday.

The spokesman, Esmail Baghaei, also defended Iran’s attacks on Gulf States, telling CNBC that targeting “military bases and assets” belonging to the United States in the region is “legitimate under international law.”

The price of crude oil has sharply spiked as the Strait of Hormuz has been effectively closed.

“As long as the situation is insecure, I think all tankers, all maritime navigation, must be very careful,” said Baghaei, who is also head of the Center for Public Diplomacy.