LONDON, July 19 (Reuters) - Oil tanker Mesdar, which had turned in the direction of Iran, was boarded by armed personnel at approximately 1630 GMT but they have now left and the vessel has resumed its voyage, its British operator said on Friday.

Britain said the Mesdar and another tanker, the Stena Impero, had been seized by Iran, making the announcement after both suddenly took up a course towards the Iranian coast.

But an Iranian news agency said the Mesdar had not been seized but had been issued a warning. Its manager Norbulk Shipping said the Liberian-registered vessel had been boarded by armed personnel and it was for a while unable to contact the vessel.

It later added: “Communication has been re-established with the vessel and Master confirmed that the armed guards have left and the vessel is free to continue the voyage. All crew are safe and well. (Reporting by Kate Holton Editing by Andrew Heavens)