The US is imposing a military blockade of the Strait of Hormuz after Iran blocked shipping during over six weeks of war in a conflict which is on hold as a fragile two-week ceasefire remains in place.

"Mr Trump wants to become the police of the Strait of Hormuz. Is this really your job? Is this the job of a powerful army like the US?" Mohsen Rezaei, a former commander-in-chief of Iran's Revolutionary Guards who was named as a military adviser by Khamenei last month, told state TV.

"These ships of yours will be sunk by our first missiles and have created a great danger for the US military. They can definitely be exposed to our missiles and we can destroy them," Rezaei, wearing his military uniform, told the state broadcaster.

Long regarded as a hardliner even within the Revolutionary Guards, Iran's ideological army, Rezaei said it would be "great" if the United States launched a ground invasion of Iran as "we would take thousands of hostages and then for each hostage we would get a billion dollars."

He also added, without giving further details: "I am not in favour of extending the ceasefire at all and this is a personal view."

A veteran and high-profile figure in Iran, Rezaei headed the Revolutionary Guards from 1981 to 1997.

The first and so far only round of Iranian negotiations with the US after the outbreak of war were led in Pakistan by parliament speaker Mohammad Bagher Ghalibaf, a former aerospace forces commander of the Revolutionary Guards.