The exercise in the Persian Gulf could begin as soon as the next two days, according to two US officials directly familiar with the latest assessment of the Revolutionary Guard's troop movements.
"We are aware of the increase in Iranian naval operations within the Arabian Gulf, Strait of Hormuz and Gulf of Oman. We are monitoring it closely, and will continue to work with our partners to ensure freedom of navigation and free flow of commerce in international waterways," Capt. William Urban, chief spokesman for US Central Command, told CNN.
The Strait of Hormuz links the Persian Gulf to the Arabian Sea. The US Energy Information Administration calls it "the world's most important oil transit chokepoint," with 20% of oil traded worldwide moving through the waterway, which is about 30 miles wide at its narrowest point.
While the US sees no immediate signs of hostile intent from Iran, the Islamic Revolutionary Guard's (IRGC) show of force has US military intelligence deeply concerned for three fundamental reasons, according to officials:
- The exercise comes as rhetoric from the IRGC towards the US has accelerated in recent days.
- It appears the IRGC is ramping up for a larger exercise this year than similar efforts in the past.
- The timing is unusual. These types of IRGC exercises typically happen much later in the year.
As of now, the US assesses the IRGC has assembled a fleet of more than 100 boats, many of them small, fast-moving vessels. It's expected Iranian air and ground assets including coastal defensive missile batteries could be involved.
Hundreds of Iranian troops are expected to participate and some regular Iranian forces could be involved as well.
The IRGC exercise comes as the US has only one major warship, the guided-missile destroyer USS The Sullivans, inside the Persian Gulf, several officials say. Other US warships are nearby, and there are numerous combat aircraft in the region.
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.
US Defense Secretary James Mattis said on Friday, "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. 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."