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 said 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 harasses U.S. Navy vessels in the Persian Gulf will be "shot out of the water," if he was elected. Trump is due to take office on Jan. 20.