Authorities in Tehran had said that the Iranian-owned oil tanker, the Sabiti, was struck on Friday. However, there has been no independent report on the cause of the damage.
During the news conference, which was broadcast on Iranian state television, Rouhani said that footage of the alleged attack existed – even though it has not yet been released.
Rouhani added that a government was behind the hit and warned that there would be consequences.
“It wasn’t an act by terrorists, by an individual, a group. It was done by a government,” Rouhani said. “It was a hostile and treacherous act.”
Images previously released by the tanker’s owner, the National Iranian Tanker Company (NITC), showed two holes above the waterline on the ship’s starboard side. They are dated Sunday.
The NITC said the alleged attack occurred 100 kilometres (60 miles) from the Saudi port of Jeddah.
The incident caused oil to spill from the tanker into the Red Sea, the company said, before it was eventually controlled and the vessel began slowly moving back towards Gulf waters.
Saudi Arabia has said it was not behind any attack on the tanker. The kingdom’s authorities said they received a distress message from the vessel, but they added that it had switched off its transponder before they could assist.
The claim could prove to be the most recent escalation in Iran’s continued standoff with Western powers and regional foes.