Armed Iranian boats attempted to stop a US-flagged oil tanker transiting the Strait of Hormuz on Tuesday, according to US officials.

Maritime security firm Vanguard Tech said that six Iranian gunboats, equipped with .50-caliber machine guns, approached the tanker as it entered the strategically vital waterway, The Caspian Post reports, citing The Wall Street Journal.

The vessels allegedly ordered the tanker to shut down its engines and prepare for boarding. Instead, the tanker accelerated and was later escorted away by a US warship.

Separately, the UK Maritime Trade Operations agency earlier reported receiving information about an incident involving a vessel roughly 16 nautical miles north of Oman, within the inbound traffic separation scheme of the Strait of Hormuz.