In a move that threatens to hugely escalate tensions between Iran and the US, British Royal Marines raided and seized an Iranian oil tanker at Gibraltar on Thursday. The tanker was accused by British officials of heading to Syria in violation of EU sanctions.

Iran’s Foreign Ministry confirmed summoning the British Ambassador to express “very strong objection to the illegal and unacceptable seizure” of the ship. Analysts expressed surprise at the unusually aggressive move against a commercial oil tanker.

British Premier Theresa May presented the raid as “firm action to enforce EU sanctions,” though Spain indicated that it was actually done because the Trump Administration asked Britain to do so. Spain said they’re looking into it, since the tanker was captured in Spanish territorial waters.

While the US hasn’t taken credit for the move yet, John Bolton was cheering the move, saying it would keep Iran from “profiting off the illicit trade,” which to be clear, is Iran shipping Iranian oil to Syria to sell it, when the US insists Iran isn’t allowed to sell any oil, and the EU says Syria isn’t allowed to buy any.