US President Donald Trump announced on Monday that the United States would charge a 20 per cent fee on all cargo passing through the Strait of Hormuz and that it is reimposing a blockade on Iranian ports. The strait, he said, would remain open "with or without" Iran, the Guardian reports.

Trump wrote that the US would be the "guardian of the Strait of Hormuz", and described the fee as compensation for "all costs required to provide security in this very unstable part of the world", CBS News reports. The blockade, he added, applies exclusively to Iranian ships and their clients, while "all other countries will have fair and open access to the strait".

The announcement comes amid a new wave of mutual attacks. The US has launched a new series of air strikes on Iran, while Tehran has stated that diplomacy has "proved futile", the Guardian writes. Iran had previously announced that it had targeted US military facilities and infrastructure in Bahrain, while the Bahraini military accused Tehran of targeting civilians with missiles and drones and announced that its air defence had intercepted multiple attacks.

Tensions escalated further on Saturday when Iran struck a container ship near the western entrance to the strait, to which the US responded with air strikes, CBS News reports. The Iranian Strait Authority declared the passage "currently unfeasible" due to American "hostile moves", and tanker traffic through the strait has once again nearly ground to a halt.

The US and Israel launched a joint military campaign against Iran in late February. A ceasefire memorandum was signed in mid-June which explicitly prohibited Tehran from charging tolls for the passage of commercial vessels, but Trump declared the truce over last week. The Iranian Embassy in Washington, on the other hand, claims that the United States has violated the agreement "from day one".

Following Trump's announcement, oil prices rose and stock indices fell, US media report.