TEHRAN — In a move that could escalate tensions between Iran and the United States, Iranian Revolutionary Guards on Monday seized a South Korean-flagged oil tanker in the crucial Strait of Hormuz.

Iranian news agencies published photos showing Guards speed boats escorting the tanker MT Hankuk Chemi and said the vessel’s crew members, including nationals of South Korea, Indonesia, Vietnam and Myanmar, had been detained. The tanker is being held at Iran’s Bandar Abbas port city.

South Korea’s foreign ministry demanded the vessel’s immediate release and said South Korean forces stationed in the Strait of Hormuz had been dispatched to the area.

The United Kingdom Marine Trade Operations, an information exchange overseen by the British royal navy in the region, acknowledged an “interaction” between a merchant vessel and Iranian authorities in the Strait of Hormuz, the narrow mouth of the Arabian Gulf through which 20 percent of all the world’s oil passes.

As a result, the UKMTO said the merchant vessel made an “alteration of course” north into Iran’s territorial waters.

The incident came before an expected visit by South Korea’s deputy foreign minister to Tehran, and against the backdrop of rising tensions between Iran and the Trump administration.

Sunday marked the first anniversary of a US drone strike that killed the top general Qasem Suleimani, and Washington has apparently been braced for possible retaliation. Both sides are watching the other warily in the final days of the Trump administration. — Agencies