On 3 July 2018, the Iranian President, Sheikh Hassan Rohani hinted at the possibility of blocking the Strait of Hormuz if unilateral US sanctions are applied against Iran. He declared that either the whole world can use the strait or noone.
Then on 5 July 2018, the Commander-in-Chief of the Guardian of the Iranian Revolution, Mohammed Ali Jafari, declared that he was all set to block the Strait of Hormuz.
While US sanctions against Iran on the sale and purchase of metal, currency, debt and the production of automobile products entered into force on 7 August, sanctions on the banking and oil sectors will apply from 5 November.
Iran had already brought up the possibility of blocking the strait in 2012. The current threat follows the failure of the negotiations that President Rohani has just tried to have with the Europeans, who oppose the US walking away from the Iran Nuclear Deal, also known as JCPoA 5 +1.
At least a third of global hydrocarbon exports cross the Strait of Hormuz.
During the mandate of George Bush (Son), the Pentagon maintained two aircraft carriers permanently in the Gulf. Now there are none. The US Fifth Fleet based in Bahrain is charged with guaranteeing free movement in the Gulf, applying the Carter Doctrine, according to which US access to hydrocarbons in the Gulf, is an issue of national security.
The spokesperson for the US Central Command  confirmed that the Pentagon was taking measures in this respect.