A US-flagged tanker was approached and challenged by Iranian gunboats in the Strait of Hormuz on Tuesday before continuing on its journey, a British maritime security firm said.The Stena Imperative was approached by three pairs of small armed boats belonging to Iran’s Revolutionary Guards while transiting the Strait of Hormuz, approximately 30km north of Oman, according to Vanguard Tech.”The vessel is now being escorted by a US warship,” the company said.The United Kingdom Maritime Trade Operations (UKMTO) — which gathers reports on threats to shipping — reported the incident and said authorities were investigating.Several small armed vessels attempted to contact the tanker via VHF radio, but it ignored the request to stop and continued on its planned route, according to the UKMTO. The agency did not specify the nationalities of the boats involved in the incident.Iran’s semi-official Fars news agency quoted unnamed officials saying that a vessel had entered Iranian waters without the required permits. The ship was warned and left the area “without any special security event taking place”, the authorities reportedly said.The Strait of Hormuz, a key passage for global transport of oil and liquefied natural gas, has been the scene of several incidents in the past.A senior naval official with the Revolutionary Guards, the ideological army of the Islamic Republic, warned last week that it could block the passage if the US launched an attack.Tensions between Tehran and Washington have sharply escalated in recent weeks. The US has increased its naval presence in the Middle East and President Donald Trump has threatened to strike Iran over its bloody crackdown on recent nationwide protests.Separately on Tuesday, Iran’s President Masoud Pezeshkian said he had instructed the country’s foreign minister to “pursue fair and equitable negotiations” with the US.Trump has repeatedly said that Iran wants to negotiate and has brought up Tehran’s nuclear programme as another issue he wants to see resolved.Washington negotiated over the programme with Tehran in multiple sessions before Israel launched a 12-day conflict with Iran last June.Trump ordered the bunker-buster bombing of three Iranian nuclear sites, most notably Tehran’s facility in Fordo, believed to be the centre of its nuclear enrichment programme.