The captain, chief officer and two second officers of the Iranian supertanker Grace 1 arrested in an operation involving British Royal Marines have been conditionally bailed without charge, the Royal Gibraltar Police have said.

The captain and his deputy were arrested on Thursday, while the other crew were arrested on Friday “as a consequence of the ongoing investigation into the suspected breach of EU sanctions on Syria,” police said in a statement.

Their arrests came after a Royal Navy warship drove off Iranian patrol boats as they attempted to impede the progress of a British tanker through the Strait of Hormuz.

That incident followed a warning by Iranian President Hassan Rouhani of unspecified “repercussions” for the seizure of the Grace 1 off Gibraltar last Thursday.

In London, ministers have urged Tehran to “de-escalate” the situation in the Gulf.

The Royal Gibraltar Police said the investigation related to the arrests is ongoing and the vessel remains in detention.