The United States launched a new wave of attacks against Iran on Wednesday, with President Donald Trump vowing to "hit them hard" after accusing Tehran's negotiators of "playing us for suckers".

The Khatam al-Anbiya command said Thursday, "any vessel traffic through the Strait of Hormuz will be targeted" adding that the strait is now "completely closed to all types of vessel", according to the Tasnim news agency.

Iran's Revolutionary Guards navy, quoted by state television IRIB and the Mehr agency, said that "two ships attempting to illegally pass through the Strait of Hormuz were hit".

"Following repeated violations of the ceasefire by the American enemy, the Strait of Hormuz will be closed until further notice," it said.

"We warn that no vessel should leave its anchorage in the Persian Gulf and the Sea of Oman. Approaching the Strait of Hormuz will be considered cooperation with the enemy."

Iranian media reported explosions across the country's south near the Strait of Hormuz, the same area where US forces had already bombarded air defence, radar and other sites on Tuesday.