Oil supertanker Grace 1 on suspicion of being carrying Iranian crude oil to Syria is seen near Gibraltar, Spain July 4, 2019. REUTERS/Stringer

MADRID (Reuters) - Gibraltar detained the supertanker Grace 1 after a request by the United States to Britain, acting Spanish Foreign Minister Josep Borrell said on Thursday.

Spain was looking into the seizure of the ship, suspected of carrying crude oil to Syria, and how it may affect Spanish sovereignty as it appears to have happened in Spanish waters, Borrell said.

Spain does not recognize the waters around Gibraltar as British.