Iran has broadened its threats against shipping in a warning from president Hassan Rouhani.

He said international waterways cannot be secure if Iran’s oil exports are halted by US sanctions, Arab News and Reuters reported.

The Iranian government has long used the threat of closure of the Strait of Hormuz, as well as recent tanker detentions there, as leverage in its cold war with the US.

“World powers know that in the case that oil is completely sanctioned and Iran's oil exports are brought down to zero, international waterways can't have the same security as before,” Rouhani said.

“So unilateral pressure against Iran can't be to their advantage and won't guarantee their security in the region and the world.”

Iranian foreign minister Mohammad Javad Zarif added that the country might act "unpredictably" in response to "unpredictable" US policies under president Donald Trump.

"Mutual unpredictability will lead to chaos," he said.