Stena Impero tanker was impounded with its 23 crew members on board at Bandar Abbas

Iran said on Sunday that the speed of its investigation into a British-flagged tanker depends on the cooperation of its crew, after ignoring calls to hand back the vessel.

The Stena Impero tanker was impounded with its 23 crew members on board at the port of Bandar Abbas after the Islamic Revolutionary Guard Corps seized it on Friday.

The Guards on Saturday released video footage showing a ship with the Stena Impero's markings being surrounded by speedboats before troops in balaclavas descend down a rope from a helicopter onto the vessel.

The Islamic republic has detained the oil tanker on allegations of failing to respond to distress calls and turning off its transponder after hitting a fishing boat.

Its crew is made up of 18 Indians, including the captain, three Russians, a Latvian and a Filipino.

"All of them are in full health, they are on the vessel and the vessel is... anchored in a safe place," said Allah-Morad Afifipoor, director-general of the Hormozgan province port and maritime authority.

"We are ready to meet their needs. But we have to carry out investigations with regards the vessel," he told Press TV.

"The investigation depends on the cooperation by the crew members on the vessel, and also our access to the evidence required for us to look into the matter.

"God willing, we will make every effort to gather all the information as soon as possible," he added.