"The weather conditions were fair. There was a little bit of snow but no wind and no ice," Commander Alex Jensen told Reuters.

"It seems as if the captain forgot to turn in the route. It happens quite often. But we don't know the actual reason why he ran aground. It could also be technical problems."

The Acushnet, which was bound for the United States, is a single-hulled tanker like the Prestige, which sank off Spain in November spilling about one-third of its 77,000-tonne cargo of fuel oil and causing Spain's worst environmental disaster.

Jensen said the Acushnet, owned by Acushnet Shipping, was on its way from Latvia with its cargo of gasoil when it ran aground last week morning.

A Danish Navy control vessel was on the scene and an environmental protection boat would arrive later in the day as a safety precaution, he said.

No member of the crew was hurt but the ship was in a sensitive marine area with seals and sea birds, Jensen said. "It's actually a very difficult area to pass through and there have been several accidents here before," he said.

It was unclear how long it would take to free the tanker, but Jensen said the ship had run hard aground and that it was up to the ship's owner to handle it.