MADRID, Aug. 15 (Xinhua) -- Gibraltar on Thursday released the Iranian oil tanker Grace 1, which was detained by British Royal Marines off the shores Gibraltar last month, Gibraltar government officials have confirmed.

The ship was boarded and taken to Gibraltar on suspicion of attempting to carry oil to Syria in "breach of EU sanctions" -- charges denied by the Iranian government.

Gibraltar's Chief Minister Fabian Picardo said he had made the decision after receiving assurances that the tanker's cargo would not be taken to Syria.

He explained that he had written assurances from Iran that the Grace 1's cargo "would not be an entity that is subject to European Union sanctions", and that in view of these assurances, "there are no longer any reasonable grounds for the continued legal detention."

The Gibraltar Chronicle newspaper also reported on Thursday that the captain of the Grace 1 and three officers had been released from arrest.