Iran was plainly looking to seize a British oil tanker Wednesday — but HMS Montrose motored to the rescue. It’s a sign of Tehran’s growing bellicosity — and not just over the 2015 nuclear deal.

The aborted hijacking was the work of several armed Revolutionary Guard boats, who’d ordered the British Heritage to sail into Iranian waters as it entered the Strait of Hormuz. Montrose, monitoring from five miles away, intervened in time.

The incident followed Iranian President Hassan Rouhani’s warning that Britain would face “consequences” for its seizure of an Iranian tanker days earlier, and other officials’ more specific threats to impound a British tanker.

Notably, the Royal Marines took custody of that Iranian ship because it was blatantly taking oil to Syria, in defiance of European Union sanctions. By attempting a reprisal, Tehran is trying to bully Britain and, by implication, the rest of Europe, into giving it a free hand in Syria.

London has urged Tehran to de-escalate, but Iran’s regional aggression has only increased since the nuke deal took effect in 2015. One more reason why the Europeans should start backing President Trump’s demand for a better bargain.