The crew of the tanker, Hancock Chemi, received a 10-20 minute warning from Iranian authorities before the troops boarded the ship, owner DM Shipping Co Ltd, told CNN in a statement on Tuesday.
The company said that its communication with the tanker was cut off once the tanker was detained.
The South Korean Foreign Ministry said five South Koreans were among the 20 civilian sailors on board the vessel. South Korean officials said in a media briefing on Tuesday that the Iranian ambassador to Seoul informed the South Korean government that the sailors on the ship were “fine.”
Seoul has sent a well-known anti-piracy unit to the Strait of Hormuz after the tanker was seized.
The Zhonghai unit, which includes South Korean special forces, arrived in the strait on Tuesday aboard the 5,000-ton destroyer Choi Yong, according to the South Korean Defense Ministry.
Tensions rose in the Persian Gulf last week, near the first anniversary of the fatal US strike on Qassem Soleimani, Iran’s top military commander.
Then on Monday, Iranian boats captured Hankuk Chemi as they crossed the Strait of Hormuz, the narrow entrance to the Persian Gulf from the Arabian Sea.
But after the seizure of the tanker, an Iranian government spokesman claimed that two years ago, South Korea froze $ 7 billion of Iranian money currently held in a South Korean bank.
“We hope that the South Korean government will release the frozen funds as soon as possible,” Ali Rabiei said on Tuesday on Iranian state television.
South Korean Foreign Ministry spokesman Choi Yong Sam said on Tuesday that the South Korean government is in close contact with its counterparts in Tehran and is trying to secure the release of the sailors and the ship.
There was no indication that the Zhonghai unit would conduct a rescue operation, as the Ministry of Defense said it would advise other ships flying the South Korean flag in the area on safety.
Founded in 2009 as South Korea’s first foreign anti-piracy force, the Cheonghai unit has been deployed in the Gulf of Aden, between Somalia and Yemen, to help maintain the free movement of South Korean ships through the region.
Roughly a year ago, Unity’s area of operations expanded to include the Gulf of Oman and the Persian Gulf, some 1,800 kilometers (1,118 miles) to the east, as tensions in the area escalated.
The expansion came after officials in the United States, a key ally of South Korea, requested assistance in protecting international shipping in the region, even though Seoul had fallen short of joining a US coalition to protect the road.
However, the unit has carried out rescue operations for South Koreans in the region before – most notably in 2011, off the coast of Somalia. In this action, commandos from the Zhonghai unit stormed a South Korean tanker that had been hijacked by a gang of Somali pirates with its crew of 21.
The South Korean Defense Ministry stated that the commandos killed eight pirates and captured five others. None of the tanker crew died.
The government said the Chunghai unit released South Korean nationals who had been captured by pirates on a merchant ship flying the Singapore flag in 2012 and supported the evacuation of South Korean nationals from Yemen in 2015.
The owner of Hankuk Chemi said in a statement on Tuesday that he was in contact with the South Korean consulate in Tehran, and expected more information later today.
The company added that it had requested the P&I Club to investigate the reservation. The insurance club is expected to send an investigator to Iran to verify the safety of the crew and examine Iran’s claims that the tanker has been detained due to environmental pollution.