A small Iranian Islamic Revolutionary Guard vessel pointed its weapon at a U.S. military helicopter in the Strait of Hormuz on Saturday, two U.S. defense officials told Reuters on Monday, an action they described as “unsafe and unprofessional.”

The incident is the latest in a series of similar actions by Iranian vessels this year, but the first reported since Republican Donald Trump won the U.S. presidential election on Nov. 8.

During his campaign, Trump vowed that any Iranian vessel that harassed the U.S. Navy in the Gulf would be “shot out of the water,” if he was elected. Trump is due to take office on Jan. 20.

The officials, speaking on condition of anonymity, said the incident took place when a Navy MH-60 helicopter flew within half a mile (0.8 km) of two Iranian vessels in international waters. One of the vessels pointed a weapon at the helicopter, the U.S. officials said.

“The behavior by our standards is provocative and could be seen as an escalation,” the officials said. At no point did the crew of the helicopter feel threatened, they added.

It was not immediately clear what type of weapon was pointed at the U.S. aircraft.

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