Iranian authorities reported that the Iranian-owned oil tanker, the Sabiti, was struck off Saudi Arabia's coast. There has been no independent report on the cause of the damage.
Iran's rival Saudi Arabia has said it was not behind any attack on the tanker. Saudi authorities said they received a distress message from the vessel, but they added that it had switched off its transponder before they could assist.
Rouhani, speaking live on state television on Monday, said the attack was undoubtedly carried out by a government and that there would be consequences.