Five armed Iranian boats tried to seize a British oil tanker in the Persian Gulf on 10 July. The British Heritage tanker was in international waters when it was approached by Iranian Revolutionary Guard boats and ordered to change course towards nearby Iranian territorial waters. A US aircraft was overhead and video recorded the incident. The UK's Royal Navy frigate HMS Montrose was escorting the tanker from the rear. It trained its deck 30mm guns, designed to drive off small boats, on the Iranians while giving verbal warnings to back away, which they did. The UK's Ministry of Defence said ‘We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region.’ The incident is yet another flashpoint in a series of maritime episodes involving Iran that have the makings of a political storm. Iran denies all charges. The US is working to strengthen maritime security in the region.