An undated picture shows the Iranian-owned Sabiti oil tanker sailing in the Red Sea.
An Iranian government spokesman on Saturday described as a "cowardly attack" an incident that Iranian media have called the apparent targeting by missiles of an Iranian-owned oil tanker and said Iran would respond after the facts had been studied.
"Iran is avoiding haste, carefully examining what has happened and probing facts," spokesman Ali Rabei was quoted as saying by the official news agency IRNA.
"An appropriate response will be given to the designers of this cowardly attack, but we will wait until all aspects of the plot are clarified," he said.
The tanker Sabiti was apparently hit in Red Sea waters on Friday, Iranian media have reported, an incident that could stoke friction in a region rattled by attacks on tankers and oil installations since May.
A senior security official said video evidence had provided leads about the incident, the semi-official news agency Fars reported.
"Piracy and mischief on international waterways aimed at making commercial shipping insecure will not go unanswered," said Ali Shamkhani, secretary of Iran's top security body, according to Fars.
Leakage of cargo from the tanker has been stopped as it heads for the Gulf, the semi-official Iranian news agency Mehr reported.
"The tanker is heading for Gulf waters and we hope it will enter Iranian waters safely," Mehr quoted an unnamed official as saying. "The cargo leakage has stopped."
The US Navy's Fifth Fleet, which operates in the region, said it was aware of the reports but had no further information.
There was no claim of responsibility for the reported incident.
Political risk consultancy Eurasia Group said it did not have firm evidence about who may have been behind the incident.
The Red Sea is a major global shipping route for oil and other trade, linking the Indian Ocean with the Mediterranean via the Suez Canal.
Crude prices jumped briefly on the news of the alleged attack and industry sources said it could drive up already high shipping costs.
