It gave no details of the date of the incident or the country where the vessel is registered.

The report comes amid faltering efforts to revive Iran's nuclear deal with world powers that would see a lifting of US sanctions on its oil exports.

The sequence of events reported by the television report left key questions unanswered.

"The United States stopped a tanker exporting Iranian oil and transferred its cargo to another tanker which it directed towards an unknown destination," it said.

"The naval arm of Iran's Revolutionary Guards then captured the tanker with air support," it said, without specifying which vessel it was referring to.

"US forces again tried to block the passage of the tanker using a warship and several helicopters but again failed.

"The tanker is now in Iranian territorial waters."

Under the 2015 nuclear deal, Washington had lifted its sanctions on Iran's oil exports in return for strict limits on its nuclear activities.

But in 2018, then president Donald Trump abandoned the agreement and reimposed the sweeping sanctions.

President Joe Biden has expressed willingness to rejoin the deal in exchange for Iran returning to the limits on its nuclear activities, but talks on the practicalities have been suspended since June.