Iranian boats attempted to seize UK tanker in the Gulf

Three Iranian vessels unsuccessfully tried to impede the passage of a British commercial vessel through the Strait of Hormuz, a British government spokesperson has said.

The British government said in a statement on Thursday that the Iranian vessels only turned away after receiving "verbal warnings" from a UK navy vessel accompanying the commercial vessel British Heritage.

"We are concerned by this action and continue to urge the Iranian authorities to deescalate the situation in the region," the statement said.

Earlier on Thursday, two US officials told Reuters news agency that five boats believed to belong to Iran's Revolutionary Guards were involved in the incident on Wednesday.

"The Royal Navy HMS Montrose, which was also there, pointed its guns at the boats and warned them over radio, at which point they dispersed," one of the officials with the knowledge of the incident said.

"It was harassment and an attempt to interfere with the passage," the other official said.

The US military confirmed the incident in a statement but declined to share any further details of the incident that comes a week after an Iranian oil tanker believed to be headed to Syria was seized by British Royal Marines off Gibraltar.

Iran denied the tanker was headed to Syria, a close ally of Tehran, while Iranian President Hassan Rouhani said Britain would face "consequences" over the tanker seizure.

"We are aware of the reports of Islamic Revolutionary Guard Corps Navy's FAC/FIAC harassment and attempts to interfere with the passage of the UK-flagged merchant vessel British Heritage today near the Strait of Hormuz," the US military's Central Command said in a statement.

"We refer you the UK Ministry of Defence for further information on this," it said.

Tensions between Iran and the US and its allies have risen sharply since Washington withdrew from the 2015 nuclear deal last year.

Since then the Trump administration has stepped up economic sanctions against Iran and moved to bring the country's oil exports to zero as part of a "maximum pressure" policy to make Iran halt actions that it said undermined regional security.

Iran has responded to the sanctions by starting to breach limits put on its nuclear activities under the nuclear deal with world powers.