US Central Command tweeted Wednesday that American forces are closely watching the developing situation, with the Iranian exercise expected to begin in the next 48 hours.
"We are aware of the increase in #Iran 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… We also continue to advocate for all maritime forces to conform to international maritime customs, standards and laws," said a trio of tweets attributed to CENTCOM spokesperson Navy Captain Bill Urban.
The Strait of Hormuz is a vital trade route, with 20 percent of the world's crude oil passing through the waterway, which is only 29 nautical miles wide at its narrowest point.
Although Iran borders the strait, it doesn't totally control it — half is claimed by Oman. Both countries have asserted the right for decades to block warships whose use of the waterway they don't consider to be "innocent passage," and Iran annually holds exercises in the strait.
​At present, the IRGC has assembled over a hundred boats, many of them fast-moving vessels, near the strait, CNN noted. Iranian air and ground forces, as well as coastal defense missile batteries, could also become involved.
US officials have indicated they see no signs of hostile intent on the part of the Iranians, but remain on high alert because of recent hostile rhetoric by the IRGC and the unusually early timing of the exercise, which is typically held in January or February.
The war of words between Iran and the US has gotten very nasty in recent weeks, with Iranian President Hassan Rouhani saying on July 22 that "America should know that peace with Iran is the mother of all peace, and war with Iran is the mother of all wars." US President Donald Trump responded later that day with an all-caps tweet, saying that Iran would "suffer consequences the likes of which few throughout history have ever suffered before… Be cautious!"
Two days later, on July 24, Iran respondedy noting, "As the dominant power in the Persian Gulf and the Strait of Hormuz, [Iran] has been the guarantor of the security of shipping and the global economy in this vital waterway and has the strength to take action against any scheme in this region," Iranian Armed Forces Chief of Staff Major General Mohammad Bagheri said, Reuters reported.
​Then last Friday, July 27, US Defense Secretary James Mattis told reporters at the Pentagon, "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."
Although Iran has stated its intent to close the waterway if the Trump administration goes forward with its plan to sanction countries that buy Iranian oil, the set of economic sanctions set to go into effect August 6 doesn't include Iran's petroleum products, only metal exports, automotive sales and debt financing, Sputnik reported. US sanctions on buyers of Iranian oil aren't due to begin until November.
Iranian naval activity has steadily increased in recent weeks in the Gulf of Oman and the Red Sea, both of which border war-stricken Yemen, where proxies of Iran, Saudi Arabia and others have engaged in the country's brutal civil war since 2015.
Saudi Arabia, Israel, the US and others have long accused Tehran of pulling the strings of the Houthis, and Israeli officials promised a military response if Iran shuts down either the Strait of Hormuz or the Straits of Bab al-Mandeb.
"If Iran tries to block the Straits of Bab al-Mandeb, it will find itself facing an international coalition determined to prevent it from doing so, and this coalition will also include the State of Israel and all its arms," Israeli Prime Minister Benjamin Netanyahu told an audience of graduating naval officers August 1, Haaretz reported.
​"I would like to emphasize: the Israeli military is ready to respond simultaneously on two fronts, and also on the Red Sea," Israeli Defense Minister Avigdor Lieberman said at the ceremony. "Only in that case, we would be less selective, and the harm to our enemies would be greater. I hope they take that into account."