The South Korean owner of a tanker detained in the Strait of Hormuz has claimed "armed" Iranian forces boarded the vessel.
The 17,400-dwt Hankuk Chemi (built 2000) was detained on Monday en route to Fujairah and taken to the Iranian port of Bandar Abbas.
The crew of 20 received a 10 to 20 minute warning of the seizure, DM Shipping said in a statement to CNN.
The shipping company said its communication with the tanker was cut off as soon as the detention took place.
Five South Korean nationals are on board, the country's foreign ministry said. Other seafarers are from Indonesia, Myanmar and Vietnam.
Iran's ambassador to Seoul told the South Korean government that the sailors who were on board "are safe", South Korean officials told reporters.
South Korea has sent an anti-piracy unit to the Strait of Hormuz.
The Cheonghae Unit, which includes special forces, arrived on Tuesday on the destroyer Choi Yong.
The handysize tanker had been underway eastbound at 12.5 knots prior to the incident, from the Petroleum Chemical Quay in Jubail, Saudi Arabia.
Iran said the vessel was seized for "creating environmental and chemical pollution in the Persian Gulf".
But Iran has also said South Korea has $7bn of Iranian funds in a domestic bank, although it has denied the detention is linked to this.
DM Shipping has denied that the vessel polluted waters in the region.
Choi Young-sam, a spokesman for South Korea's foreign ministry, said the South Korean government is in close communication with counterparts in Tehran and is trying to secure the release of the seafarers and the tanker.
