South Korea says it will send a delegation to Iran “at the earliest possible date” to try to negotiate the release of an oil tanker seized by Iran’s Revolutionary Guards on Monday.
Iran says the ship violated pollution rules, which its operators deny.
Meanwhile, a South Korean warship with an anti-piracy unit has moved close to the Strait of Hormuz.
The incident comes amid tensions over Iranian funds frozen in South Korean banks because of US sanctions.
“A delegation… will be dispatched to Iran at the earliest possible date to try to resolve the matter through bilateral negotiations,” foreign ministry spokesman Choi Young-sam told reporters.
A previously arranged visit to Iran by Vice-Foreign Minister Choi Jong-kun will still go ahead early next week, he added.
The MT Hankuk Chemi has a crew of 20 which includes nationals from Indonesia, Myanmar, South Korea and Vietnam.
Foreign Minister Kang Kyung-wha declined to speculate on reports that Iran seized the ship to try to pressure Seoul into unlocking Iranian assets.
“We need to verify the facts first and ensure the safety of our crew,” she told reporters. “We are making diplomatic efforts for an early release.”
On Tuesday South Korea’s defence ministry said a destroyer carrying an anti-piracy unit was in waters close to the Strait of Hormuz – a narrow shipping route in the Gulf region close to where the tanker was seized – to “ensure the safety” of South Korean nationals.
The warship has been in waters off Somalia since late last year to counter piracy attacks in the Gulf of Aden and the Strait of Hormuz, Yonhap news agency reported.
In a statement, Iran’s foreign ministry spokesman said the tanker’s seizure was over a “purely technical issue and due to polluting the sea”.
The ship’s operator has denied that the vessel was polluting waters.
An Iranian government spokesman strongly denied any suggestions that the seizure was a form of “hostage-taking” linked to Iranian funds being held by South Korea.
“We’ve become used to such allegations … but if there is any hostage-taking, it is Korea’s government that is holding $7bn (£5bn) which belongs to us,” Ali Rabiei told reporters at a news conference.
The incident marks the first Iranian seizure of a major vessel in more than a year.