By Kyu-seok Shim

SEOUL, May 11 (Reuters) - South Korea's presidential Blue House on Monday condemned in the strongest terms an attack against a ‌cargo ship operated by a Korean shipper this month in the ‌Strait of Hormuz and said it plans to respond once the source of the attack is ​identified.

Experts conducted an initial forensic analysis of the damage to the port stern, a Blue House official said. The attack had led to a fire in the vessel's engine room.

Namu, the vessel operated by the shipper HMM Co., was ‌not in violation of any ⁠rules in effect at the time in the waters off the United Arab Emirates and it was a case of ⁠an attack against a commercial vessel that cannot be justified, the official said.

"We condemn this in the strongest terms," Wi Sung-lac, the South Korean presidential national security ​adviser, told ​a news briefing. Damage to the ​vessel was identified in the forensic ‌inspection by South Korean officials and experts at a port in Dubai, Wi said.

The damage was not known earlier following the attack due to its position in the lower port stern, according to a Blue House official.

It was not known what role, if any, Iran may have had in the attack, ‌the official said. Tehran has previously denied ​any responsibility for the attack that involved a ​strong impact on the side ​of the vessel.

On Monday, the Iranian embassy in South Korea ‌said in a statement it did ​not have any ​position on the matter but would announce if there is any update or official position.

U.S. President Donald Trump said soon after the incident that ​Iran had fired at ‌the South Korean vessel, and urged Seoul to join U.S.-led efforts ​to secure shipping through the strait.

(Reporting by Kyu-seok Shim, Jack Kim ​and Heejin KimEditing by Ed Davies)