South Korea relies heavily on Middle Eastern fuel imports, most of which transited through Hormuz until US-Israeli attacks on Iran in late February prompted Tehran to effectively shut the strait.

The arrival of the Malta-flagged Odessa, carrying one million barrels of crude oil, will likely ease Seoul's concerns over energy security as the war in the Middle East drags on.

The hulking vessel was spotted at around 10:00 am (0100 GMT) near a mooring facility off the coast of Seosan, according to AFP reporters.

Its arrival is expected to help stabilise supply, securing crude equivalent to nearly half of South Korea's daily oil consumption, industry sources told AFP.

Its cargo will undergo refining before being supplied to the market as petroleum products, including gasoline and diesel, the sources said.

The Odessa passed through the Strait of Hormuz on April 17, a source told AFP, during a brief reprieve in the blockade.

Traffic through the waterway has plummeted since the war, with the United States and Iran trading fire in the area on Thursday, threatening a fragile ceasefire.

The months-long conflict has prompted South Korea, a major petrochemicals producer and refiner, to impose a fuel price cap for the first time in nearly 30 years.

It has also sought to diversify its fuel supply, securing more than 270 million barrels of crude -- sufficient for more than three months of its oil needs -- via routes unaffected by the blockade.

Around 1,500 ships and 20,000 international crew are trapped in the Gulf region because of the conflict, the secretary-general of the UN's International Maritime Organization, Arsenio Dominguez, said Thursday.

US President Donald Trump briefly launched a naval operation this week to force open the strait to commercial vessels, only to stand it down within hours, citing progress on negotiations with Iran.

He also accused Iran of attacking a South Korean-operated cargo ship in the strait this week, an act denied by Tehran's embassy in Seoul.

The fire-damaged HMM Namu arrived at port in Dubai on Friday, its operator told AFP.

The vessel will "soon be investigated", an HMM spokesperson said.