US tells Gulf vessels to stay clear of warships, in thinly-veiled warning to Iran
The notice to mariners in the Gulf follows a heated confrontation last month between Washington and Tehran, with President Donald Trump threatening to fire on any Iranian ship that "harasses" navy vessels.
"Armed vessels approaching within 100 meters of a US naval vessel may be interpreted as a threat," the alert, first reported by Reuters, reads.
The alert does not constitute a change of the US military's rules of engagement, an official told Reuters.
Instead, the message is intended to "enhance safety, minimise ambiguity and reduce the risk of miscalculation", the US Naval Forces Central Command said in a statement.
In April, the US Navy accused Iranian forces of "dangerous and provocative actions" after it said 11 Iranian Revolutionary Guards Corps (IRGC) vessels repeatedly approached naval ships at "extremely close range and high speeds".
Tehran rejected the allegations, which it described as a "Hollywood version of events". The IRGC in turn accused the US Navy of "dangerous" behaviour and warned it would also respond "decisively" if needed.
Tensions between the two arch foes have escalated since Washington withdrew from a landmark nuclear deal and reimposed sanctions on Iran in 2018.
They reached fever pitch when the US killed IRGC top commander Qasem Soleimani in a drone strike in January, sparking fears of a full-scale war.
Iran later retaliated by firing a volley of ballistic missiles at Iraqi bases hosting US troops, injuring dozens of personnel.
A spate of tanker seizures and attacks on oil infrastructure hit the Gulf last year, with the US and its allies in the region - Saudi Arabia and the UAE - mainly blaming the incidents on Iran.