The crew of the seized tanker Stena Impero are safe, the vessel’s owners said, after direct communication with them in Iran.

The British-flagged vessel was taken by Iran’s Revolutionary Guard on Friday amid heightened tensions between Tehran and the West.

Stena Bulk confirmed it had now had direct contact with the crew of the impounded vessel.

The ship’s master said they were all safe and there had been good cooperation with the Iranian personnel on board.

Stena Bulk said the crew’s family members were being kept updated on the latest developments and being offered the firm’s full support.

Erik Hanell, president and CEO of Stena Bulk said: “We do of course appreciate this step of development and that this is a first sign that we will soon see more positive progress from the Iranian authorities.”

The development came as the head of the Iranian supreme leader’s office said the UK was sending a mediator to negotiate for the release of the vessel.

“A country that at one time appointed ministers and lawyers in Iran has reached a point where they send a mediator and plead for their ship to be freed,” Mohammad Mohammadi-Golpayegani said, according to the semi-official Tasnim news site.

UK sources insisted they were not aware of any mediator being sent to Iran, insisting that diplomatic contacts were through the ambassador and embassy in Tehran.

The issue will be one of the first diplomatic challenges confronting incoming prime minister Boris Johnson.

Tehran has claimed the tanker collided with a fishing boat, while the UK has accused Iran of “state piracy”.