Gibraltar had seized an Iranian oil tanker suspected by the UK of carrying two million barrels of crude oil to Syria.

Police in Gibraltar said officers have arrested the captain and chief officer of the Iranian oil tanker Grace 1, which was seized off the British-controlled territory last week for suspected breach of EU sanctions against Syria.

The arrests follow “a protracted search of the vessel, where documents and electronic devices have been seized and examined”.

According to the police, the tanker remains impounded as the investigation is “still ongoing”.

The vessel was intercepted by the British overseas territory on the southern tip of Spain on July 4. A senior Spanish official said the operation was requested by the United States.

The EU and others have imposed sanctions on Syrian President Bashar al-Assad‘s government over its continued crackdown against civilians.

Iranian President Hassan Rouhani warned that the UK would face “repercussions” for seizing the Iranian oil tanker.

The British government said the tanker was believed to be carrying two million barrels of crude oil to Syria.

Tehran denied that the tanker was bound for Syria and its seizure as “piracy”. It also summoned the British envoy in Iran to protest against the action.