The US state department has confirmed it offered millions of dollars to the captain of an Iranian oil tanker which is at the centre of a diplomatic row. Brian Hook, head of the department's Iran Action Group, emailed the captain of the Adrian Darya 1 about sailing it somewhere the US could seize it. The vessel was suspected of moving oil to Syria, and was temporarily impounded by UK authorities in Gibraltar in July. It was released last month after Iran gave assurances about its destination. The US justice department, which had tried to block the release, then issued a warrant to seize the tanker. Reports of the cash offer first appeared in the Financial Times on Wednesday and have been confirmed by the state department. "We have conducted extensive outreach to several ship captains as well as shipping companies," a spokeswoman told AFP news agency. The US blacklisted the tanker last Friday. A treasury department statement said the vessel was being used to transport 2.1 million barrels of Iranian crude oil for the benefit of Iran's Revolutionary Guard - a branch of the country's armed forces the US has designated a terrorist organisation.