MADRID, Aug. 19 (Xinhua) -- The Iranian oil tanker seized by Britain for weeks has left Gibraltar for international waters, Iran's Ambassador to Britain Hamid Baeidinejad confirmed Monday.

"At this point, we confirm that ... the Iranian oil tanker began to move towards international waters," Baeidinejad wrote on his personal Twitter account.

Data from ship-tracking service MarineTraffic showed that the Iran-flagged Adrian Darya 1, new name for the captured Grace 1 oil tanker, set sail shortly before midnight on Sunday towards international waters and is now headed for the Greek port of Kalamata, according to media reports.

Gibraltar on Thursday released the tanker and later turned down the U.S. request to retain it.

Gibraltar said the United States wanted to seize the vessel, which was carrying 2.1 million barrels of oil, on the grounds that it was "intrinsically linked" to the U.S. sanctions against Iran.

The oil taker was detained in July off the coast of the British Overseas Territory of Gibraltar by Royal Marines on suspicion of attempting to carry oil to Syria "in breach of EU sanctions," charges denied by the Iranian government.