Tehran, Iran - Iran's Revolutionary Guards said on Wednesday that their naval forces stopped two ships attempting to cross the Strait of Hormuz amid an ongoing blockade.

The seizures come as Iranian ports themselves remain under a naval blockade imposed by the US on April 13, days after a ceasefire was announced that paused President Donald Trump's war on Iran.

"The Islamic Revolutionary Guard Corps naval force this morning identified and stopped in the Strait of Hormuz two violating ships," the IRGC said in a statement.

"The two offending ships... were seized by the IRGC's naval forces and directed to the Iranian coast," it added, although it was not immediately clear if the Guards boarded them.

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One ship was identified as MSC-FRANCESCA, which the Guards said belonged "to the Zionist regime" in reference to Israel, and the other as "EPAMINONDAS", which was "tampering with navigation systems and jeopardising maritime security."

The IRGC further warned against any action against the regulations imposed by the Islamic republic in the strait, "as well as activities contrary to the safe passage" through the waterway.

Iran has said vessels must seek permission to leave or enter the Gulf through Hormuz, a route that in peacetime accounts for a fifth of the world's oil and gas exports along with other vital commodities.

The temporary Iran-US truce was hours from expiring on Tuesday before Trump announced an extension to facilitate more negotiations. Iranian officials have refused to hold a new round of talks until the US blockade is lifted.