The ministry’s citizen protection director, Judha Nugraha, said the Indonesian Embassy in Tehran had sent a diplomatic notice to the Iranian government requesting consular access to the seized tanker.

Two Indonesian nationals, identified only as AW and MA, were working aboard the MT Hankuk Chemi as it was seized in the Persian Gulf.

“Indonesian Embassy in Iran officers in Bandar Abbas have visited the ship and its crew. The [Indonesian] crew members were safe,” Judha told The Jakarta Post on Wednesday.

He said the ministry had contacted the seafarers’ employer to help them get in touch with their families.

It remains to be seen what can be done to get the crew members out of the diplomatic row between South Korea and Iran.

In a separate statement, the Indonesian Embassy in Tehran said it would continue to keep tabs on the two Indonesian nationals in coordination with the relevant authorities.

Previously, South Korean news agency Yonhap reported that the oil tanker was travelling to the United Arab Emirates with 20 crew members on board: 11 Myanmar nationals, five South Koreans, two Indonesians and two Vietnamese citizens.

South Korea said on Tuesday that it would send a delegation to Iran to negotiate the release of the seized oil tanker and its crew as a South Korean antipiracy vessel arrived in the waters near the Strait of Hormuz.

Iran's Revolutionary Guard said on Monday that it had seized the South Korean-flagged vessel – which it said was carrying 7,200 tons of "oil chemical products" – for violating maritime environmental laws, AFP reported.

Seoul's defense ministry said on Tuesday that a destroyer carrying members of South Korea's anti-piracy unit had arrived in the waters near the Strait of Hormuz and was "carrying out a mission to ensure the safety of our nationals", without giving details.

The 300-strong Cheonghae unit had been in the region since late last year and would not engage in an offensive operation, an unnamed military official told Yonhap.

"The issue should be resolved through diplomacy. The unit is focused on the safety of our people who use the waterway after the seizure incident," the official added.

Foreign ministry spokesman Choi Young-sam said a government delegation would be “dispatched to Iran at the earliest possible date to try to resolve the matter through bilateral negotiations”.

South Korea's vice foreign minister Choi Jong-kun will go ahead with a planned three-day trip to Tehran early next week, the spokesman added.

The vice minister's visit had been arranged prior to the seizure, as Tehran seeks the release of billions of dollars held in Seoul under US sanctions.

According to Iran's central bank governor Abdolnasser Hemmati, the country has "$7 billion of deposits in South Korea" that can neither "be transferred nor do we get any returns on, while they ask us for the costs" of holding the funds.

South Korean foreign minister Kang Kyung-wha did not comment on speculation that Iran had seized the ship in a bid to pressure Seoul to unlock Iranian assets.

"We need to verify the facts first and ensure the safety of our crew," Kang told reporters, as quoted by AFP.

"We are making diplomatic efforts for an early release," she added.