A merchant vessel transiting the Strait of Hormuz was hailed by multiple small armed craft on Monday in an encounter now under investigation, according to a maritime security advisory from United Kingdom Maritime Trade Operations(UKMTO).

The incident occurred at approximately 0900 UTC on February 3 within the inbound traffic separation scheme of the strategic waterway, about 16 nautical miles north of Oman. UKMTO said the vessel declined demands to stop and continued along its planned route.

Martin Kelly, Head of Advisory at EOS Risk Group, described the encounter as “IRGC flexing in the SoH,” referring to Iran’s Islamic Revolutionary Guard Corps and the Strait of Hormuz. Kelly noted that the IRGC regularly hails vessels in the strait, but added that “against the current backdrop, tensions are understandably higher.”

The incident comes days ahead of a scheduled round of U.S.-Iran nuclear negotiations set for Friday in Istanbul. The talks follow a period of heightened tensions, including a U.S. naval buildup near Iran after deadly anti-government protests last month.

President Trump has positioned U.S. warships off Iran’s coast and warned publicly that “bad things would probably happen” if negotiations fail. The United States struck Iranian nuclear facilities in June 2025, after which Iran said it halted uranium enrichment.

The upcoming talks face major obstacles. Washington is demanding zero uranium enrichment, limits on Iran’s ballistic missile program, and an end to support for regional proxy groups—conditions Tehran has rejected as violations of sovereignty.

Iran has also called for U.S. military assets to be withdrawn from nearby waters before negotiations begin, a demand that appears unlikely to be met given the current naval posture.

UKMTO has advised vessels transiting the area to proceed with caution and report any suspicious activity.

The Strait of Hormuz remains one of the world’s most critical maritime chokepoints, carrying roughly one-fifth of global oil supply. Any sustained disruption to shipping through the strait would have immediate consequences for global energy markets and international trade.