Western navies held a series of drills off the coast of Iran last week, in a show of force in light of increased Iranian harassment of foreign military vessels.

The exercises, dubbed “United Trident,” were led by the United Kingdom and included ships from the US, France and Australia. The navies practiced fighting off enemy aerial incursions and mine clearing, as well as live fire drills, according to the British daily Telegraph.

The final drill featured 13 ships from the allied navies sailing in formation, with helicopters flying overhead.

British naval officials told the Telegraph that the drills had been planned for some time and were not connected to US President Donald Trump’s recent adoption of a more hardline stance against Iran, which resulted in the imposition of sanctions Friday on a number of individuals and entities involved in the country’s ballistic missile program. Rather, they said, they were rather meant to promote stability in the Persian Gulf and to ensure “the free flow of commerce” through the Strait of Hormuz.

Satellite view of the Strait of Hormuz (photo credit: NASA/Public domain)

Satellite view of the Strait of Hormuz (photo credit: NASA/Public domain)

The strait is a narrow waterway connecting the Persian Gulf to the Indian Sea through which a fifth of the world’s oil supply passes.

Iran has previously threatened to close off the strait in the past over tensions with the US, a move that would lead to turmoil in global oil markets.

Last week, Iranian Navy Commander Rear Admiral Habibollah Sayyari was dismissive of the show of force close to Iranian waters, telling the semi-official Mehr news agency that “they talk a lot.”

He also warned the Western navies against encroaching on Iranian waters, saying, “This is our red line.”

Iran has had numerous confrontations recently with US Navy ships in the Persian Gulf and around the Strait of Hormuz, with the most notable case being Iran’s capture last January of 10 US Navy sailors who had drifted into Iranian waters after experiencing mechanical problems.

File photo of the USS Mahan destroyer, seen in September 2002. (Public Domain/Photographer's Mate Airman Rex Nelson, US Navy/Wikipedia)

File photo of the USS Mahan destroyer, seen in September 2002. (Public Domain/Photographer’s Mate Airman Rex Nelson, US Navy/Wikipedia)

Earlier this month a US Navy vessel fired three warning shots at a group of Iranian ships that approached the destroyer at high speed in the strait.

US defense officials said the USS Mahan called on the four Iranian Revolutionary Guard Corps vessels to slow down, but they continued to approach at high speed. This led the ship to fire flares and a helicopter dropped a “smoke float” signaling device, according to Reuters.

Agencies contributed to this report.