Strait of Hormuz
Strait of HormuzThinkstock

The US Department of Transportation's Maritime Administration has issued a new warning to commercial shipping about Iranian threats in the Strait of Hormuz and Persian Gulf, saying that some ships have reported having their GPS interfered with, CNN reported on Wednesday.

Additionally, the administration warned that there have been reports of "unknown entities falsely claiming to be US or coalition warships."

The warning, issued Wednesday, listed a series of incidents involving Iran since May, including Iran's seizure of the United Kingdom-flagged M/V STENA IMPERO and the detention and subsequent release of the Liberian-flagged M/V MESDAR.

The warning says that during "at least two" recent encounters involving Iranian military forces, "vessels reported GPS interference. One vessel reportedly shut off its Automatic Identification System (AIS) before it was seized, complicating response efforts."

"Vessels have also reported spoofed bridge-to-bridge communications from unknown entities falsely claiming to be US or coalition warships," the warning adds, according to CNN.

US Central Command, which oversees US military operations in the region, issued a statement Wednesday saying, "Vessels have reported GPS interference, bridge-to-bridge communications spoofing, and/or other communications jamming with little to no warning."

"The US remains committed to working with allies and regional partners to safeguard the freedom of navigation, the free flow of commerce, and the protection of US vessels and personnel in this region," the statement added.

A US defense official told CNN that Iran has placed GPS jammers on Iran-controlled Abu Musa Island, which lies in the Persian Gulf close to the entrance of the Strait of Hormuz.

The official said that Iran had placed the jammers at that location in an attempt to disrupt civilian aircraft and ship navigation systems, hoping ships or planes will mistakenly wander into Iranian waters or airspace while their GPS systems were not functioning properly, giving Iranian forces the pretext needed to seize them.

The official said the Iranian jammers have no effect on US military warships and aircraft.

The report comes amid ongoing tensions between the US and Iran in the Persian Gulf. In June, Iran shot down a US drone, claiming it violated Iranian airspace near the Strait of Hormuz.

US President Donald Trump announced several weeks ago that a US ship had destroyed an Iranian drone near the Persian Gulf.

Iran, however, denied Trump’s claims, with its Deputy Foreign Minister, Abbas Araghchi, tweeting, “We have not lost any drone in the Strait of Hormuz nor anywhere else. I am worried that USS Boxer has shot down their own UAS by mistake!”