On Saturday, several fast-attack boats of the Iranian Revolutionary Guards Corps (IRGC) approached a U.S. Navy ship in the Strait of Hormuz at high speed in the latest “unsafe and unprofessional” action by Iranian forces.

A U.S. official told Reuters about the incident on Monday:

The official, speaking on the condition of anonymity, said the IRGCN boats came within 600 yards of the USNS Invincible, a tracking ship, and stopped. The Invincible was being accompanied by three ships from British Royal Navy and forced the formation to change course.

The official said attempts were made to communicate over radio, but there was no response and the interaction was “unsafe and unprofessional.”

“The Invincible is a Stalwart class ocean surveillance ship – known as a tracking ship – that is equipped with antennas and electronics to support the tracking and launching of missiles and rockets,” explains Radio Free Europe.

CBS News notes this was the second close encounter between the Invincible and Iranian naval forces in just two days:

The “unsafe” encounter came just two days after an Iranian navy frigate came within 150 yards of the Invincible in the Gulf of Oman, just south of the Strait of Hormuz. The gulf separates Oman from southeastern Iran.

The earlier encounter was deemed “unprofessional” but not unsafe because the frigate maintained a parallel course with the Invincible at the point of closest approach. The Saturday incident was also more worrying as it involved the elite Revolutionary Guard unit.

According to Fox News, Iran test-fired a pair of ballistic missiles into the Gulf of Oman over the weekend. It was the first time Fateh-110 short-range ballistic missiles have been tested in two years. One of the missiles successfully destroyed a target barge at a range of 155 miles.

One of the missiles launched from the IRGC base in Bandar-e-Jask successfully destroyed a target barge at a range of 155 miles. The other missed its target. U.S. officials told Fox News the latest version of the Fateh-110 missile has an “active seeker” system that helps it target ships at sea.

Sky News recalls that President Donald Trump “vowed that Iranian ships which intimidate the U.S. Navy would be ‘shot out of the water'” during his presidential campaign.