Ali Abdollahi, commander of Iran’s Khatam al-Anbiya Central Headquarters, said continued US action creating “insecurity” for Iranian shipping would amount to “a prelude to a violation of the ceasefire”.

He warned Iran’s armed forces would not allow “any exports or imports” through the Persian Gulf, the Sea of Oman or the Red Sea.

The United States imposed the blockade on Monday following failed talks with Iran in Pakistan aimed at ending weeks of conflict.

On Wednesday, the US military said no ships had passed the blockade in its first 24 hours, with six merchant vessels turned back in the Gulf of Oman.

The ceasefire was announced on April 8, after nearly six weeks of fighting involving Iran, the US and Israel.

Despite US claims, there are signs the blockade may not be fully effective. Tracking data indicated some vessels had already crossed the Strait of Hormuz, a critical artery for global energy supplies.

Iranian media, including Tasnim news agency, said commercial shipping from southern ports had continued over the past 24 hours.