Iranian ships 'force' US and Royal Navy vessels to change course Published duration 6 March 2017

image copyright Reuters image caption The USNS Invincible, pictured here in 2012, was forced to change course

A US Navy ship was forced to change course when fast-moving Iranian vessels approached it in the Strait of Hormuz, US officials say.

The USNS Invincible changed direction when the other vessels came within 600 yards (550m) before stopping.

Three British Royal Navy vessels, accompanying the American ship at the time, were also forced to move.

A US official told reporters the Iranian vessel had tried to position itself between them.

The Iranian ships are believed to belong to the Revolutionary Guard Corps.

Speaking on condition of anonymity, a navy official told the Associated Press news agency that such incidents had been happening on a regular basis.

The navy considers them "unprofessional and dangerous", and had fired warning shots in previous incidents, he added.

The Invincible, a tracking ship, is fitted with considerable radar equipment and other scientific instruments.

Such ships are usually deployed to monitor missile launches and provide important data back to the command centre. For friendly launches, such data helps with accuracy and future weapon design.

But the system can also be used to track foreign missile launches and tests.

That test led to sanctions from the United States and a strongly-worded warning from President Donald Trump.

"Iran is playing with fire - they don't appreciate how 'kind' President Obama was to them. Not me!" he tweeted.