Iran has said that the oil tanker Britain intercepted in Gibraltar on Thursday was not headed for Syria.
Deputy foreign minister Abbas Araghchi said on Sunday that the Iranian tanker’s “destination was not Syria”.
He added that there was no law allowing authorities in Gibraltar to stop the tanker and called it “piracy”.
Authorities intercepted the supertanker Grace 1, saying they believed it to be violating European Union sanctions by carrying a shipment of Iranian crude oil to Syria.
A detachment of Royal Marines from 42 Commando boarded the vessel in a joint operation with the Royal Gibraltar Police.
Spanish authorities said the seizure came at the request of the US.
Britain’s ambassador in Tehran, Rob Macaire, was summoned to the Iranian Foreign Ministry to explain the UK government’s actions.
The incident occurred amid heightened tensions over Iran’s unravelling 2015 nuclear deal with world powers, which the US withdrew from last year.