Iran's Islamic Revolutionary Guard Corps (IRGC) said the Strait of Hormuz was closed as of the evening of the 18th (local time).
In a statement posted the same day on its own propaganda outlet, Sepah News, the IRGC Navy said, "Any attempt to approach the Strait of Hormuz will be regarded as cooperation with the enemy, and the vessel in question will become a target of attack."
The IRGC cited the United States' violation of the two-week truce that began on the 8th—such as not lifting the blockade on Iranian ships and ports—as the reason for this move. It also stressed that the strait will not reopen until the United States lifts the maritime blockade.
They argued that U.S. President Donald Trump's statement regarding the Strait of Hormuz is not trustworthy and called on ships and owners to follow official guidance issued through IRGC channels and emergency frequency (VHF channel 16).
Earlier, Iranian Foreign Minister Abbas Araghchi said the previous day, after the cease-fire announcement between Israel and Lebanon, that "all merchant vessels transiting the Strait of Hormuz will be fully permitted to sail during the remaining cease-fire period."
However, the next day, Khatam al-Anbiya Central Headquarters, which has unified command over Iran's armed forces, referred to the U.S. blockade against Iran and announced that the military would again control ship traffic in the Strait of Hormuz.
The Central Headquarters said, "The United States repeatedly violates its promises and continues acts of piracy and plunder under the pretext of a so-called 'blockade,'" adding, "Accordingly, control of the Strait of Hormuz has returned to its previous state, and the strait is now under the strict management and control of the Iranian military."
When the Strait of Hormuz was temporarily opened, more than 10 oil tankers reportedly passed through. But after the Iranian military declared the reimposition of the blockade that day, reports that oil tankers and container ships were hit were filed one after another with the United Kingdom Maritime Trade Operations (UKMTO).