Ships travelling through the Strait of Hormuz are being warned by a security organisation to stay as far possible from Iranian waters to avoid being seized.
The Bahrain-based, US-backed International Maritime Security Construct warned vessels to steer clear of Iranian territorial waters, the Associated Press reported, as tensions bubble between Iran and the US.
US Navy Commander Timothy Hawkins, a spokesman for the 5th Fleet, acknowledged the warning had been given, but declined to discuss specifics.
A European Union-led maritime organisation has separately “warned of a possibility of an attack on a merchant vessel of unknown flag in the Strait of Hormuz in the next 12 to 72 hours”, said private intelligence firm Ambrey.
More than 3,000 American sailors and marines arrived in the Middle East last Monday as the US strengthens its presence in the region.
The warnings to shipping and increased tensions come despite news of a potential deal between Iran and the US over prisoners being held in Tehran.
The IMSC “is notifying regional mariners of appropriate precautions to minimise the risk of seizure based on current regional tensions, which we seek to de-escalate,” Cmdr Hawkins said.
“Vessels are being advised to transit as far away from Iranian territorial waters as possible.”
In its statement, Ambrey said: “Previously, after a similar warning was issued, a merchant vessel was seized by Iranian authorities under a false pretext.”
Iran, through its state media, did not acknowledge any new plans to intercept vessels in the strait and its mission to the United Nations did not immediately respond to a request for comment, AP reported.
Similar warnings went out to shipping companies earlier this year before Iran seized two tankers travelling near the strait, where 20 per cent of the world's oil passes.
The US navy said its increased presence “brings to the region additional aviation and naval assets, as well as more US marines and sailors, providing greater flexibility and maritime capability to US 5th Fleet”.
Among the ships reaching the Red Sea on Monday were the USS Bataan and USS Carter Hall.
The deployment captured Iran's attention, with its chief diplomat telling neighbouring nations that the region does not need “foreigners” providing security.
Last week, Iran’s Islamic Revolutionary Guard Corps launched a surprise military drill on disputed islands in Gulf waters.
The Strait of Hormuz is in the territorial waters of Iran and Oman, and at its narrowest point is just 33 kilometres wide. The width of the shipping lane in either direction is only 3km.
Anything affecting it ripples through global energy markets.