A British frigate positioned itself between three Iranian Revolutionary Guard gunboats and an oil tanker in the Persian Gulf overnight Wednesday, forcing the Iranian craft to withdraw.

The Isle of Man registered British Heritage tanker had been transiting the Persian Gulf and entering the narrow Strait of Hormuz, one of the most strategically important, crowded, and contested waterways on earth when it was ordered into Iranian waters. A Ministry of Defence spokesman Thursday said three Iranian vessels had been attempting to intercept the British tanker to make it comply.

HMS Montrose, a British frigate of the Type 23 class positioned itself between the tanker and the intercepting craft, and forced the Iranians to withdraw. A British government statement claims the warship issued verbal warnings, but U.S. news network CNN cited military contacts “with direct knowledge of the incident” which said the frigate trained its deck guns on the Iranian craft.

The report further claims the incident was captured by a U.S. aircraft observing the incident recorded footage of the confrontation.

The Ministry of Defence said Thursday:

Contrary to international law, three Iranian vessels attempted to impede the passage of a commercial vessel, British Heritage, through the Strait of Hormuz. HMS Montrose was forced to position herself between the Iranian vessels and British Heritage and issue verbal warnings to the Iranian vessels, which then turned away. We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region.

Iran has denied responsibility for the incident, with a statement claiming “there were no clashes with alien boats, especially English boats”, reports the Associated Press.