The stern of a bulk carrier operated by South Korean shipper HMM was struck by two unidentified objects on May 4 while stranded in the Strait of Hormuz, the foreign ministry said on Sunday.
A week ago, Seoul reported a blast and fire aboard the same vessel - the HMM Namu - in the strait, while anchored near the United Arab Emirates. No one was harmed in the incident.
US President Donald Trump said at the time the incident was caused by an Iranian attack.
Seoul was investigating the incident, and the vessel was towed to a port in Dubai after the blaze on Monday, while an on-site inspection was conducted on Friday.
It was not certain what the objects were, though they were captured on surveillance camera, the ministry said. Authorities said debris would be collected at the site for analysis.
The objects hit the left stern at around 15:30 Monday, Park Il, the ministry's spokesperson said on Sunday.
The strike caused a blaze that damaged a seven-by-five-metre area, Park said, adding that the incident was unlikely to have been caused by a sea mine or any problems with the vessel's engine, generator or boiler.
"We assume the cause of the fire was irrelevant to internal issues on the ship," he said.
South Korea was in contact with relevant countries, including Iran, over the incident, Park said.
Iran has denied responsibility. It did not immediately respond to a request for comment on the objects outside of normal business hours.
An HMM spokesperson declined to comment.
(Reporting by Heejin Kim. Editing by Bernadette Baum)
