Washington(CNN) Iran has begun a major military exercise in the Persian Gulf region according to a US defense official directly familiar with the latest US information.
The "exercise is underway," and the US assesses the Islamic Revolutionary Guard Corps has deployed "dozens" of small boats in the initial phase. The exercise is taking place in the Persian Gulf, the Strait of Hormuz and the Gulf of Oman.
While Iran has not widely publicized the exercise, the US military is concerned it could demonstrate Iran's ability to interfere with commercial shipping and shut down the Strait of Hormuz, a crucial conduit for global energy supplies, US officials say.
The timing is unusual. These types of IRGC exercises typically happen much later in the year and the official said the US assesses that the exercise is partly being held in response to rising rhetoric from the US.
The official said it's not clear if the timing of the exercise is tied to the US only having one warship inside the Gulf at this time. US military commanders are "monitoring the situation closely" a second official said. Additional US Navy ships are expected to move the Strait of Hormuz and into the Gulf in the coming days officials say.
The US military has been trying to encourage other nations in the region, especially Saudi Arabia, to take a strong line on keeping the Gulf open in the face of rising Iranian rhetoric. They have also expressed concern about keeping open the waterways off Yemen where Iranian-backed rebels have attacked oil tankers.
"Iran has threatened to close the Strait of Hormuz. They've done that previously in years past. They saw the international community put -- dozens of nations of the international community put their naval forces in for exercises to clear the straits," said US Defense Secretary James Mattis last week. "Clearly, this would be an attack on international shipping, and -- and it would have, obviously, an international response to reopen the shipping lanes with whatever that took, because of the world's economy depends on that energy, those energy supplies flowing out of there."
Tensions between the two nations increased after the US withdrew from the Iran nuclear deal in May. The Trump White House has moved to reinstate sanctions on Tehran in two major tranches. Some will be reimposed in August and target autos, gold and other key metals, while others will snap back in November and target the energy sector and transactions with Iran's central bank.