in Gibraltar have arrested the captain and chief officer of the detained
Iranian Grace 1 supertanker accused of violating EU sanctions on Syria.
Documents and electronic devices were also seized from the vessel during the operation.
Last week, British Royal Marines boarded the tanker off Gibraltar and seized it on suspicion that it was breaking EU sanctions by taking oil to Syria.
"The investigation is still ongoing and the Grace 1 remains detained," police said in a statement on Thursday.
The two men, both Indian nationals, were arrested on Thursday afternoon and interviewed.
Neither has been charged, according to reports.
In a statement, the Royal Gibraltar Police said the arrests followed a "protracted" search of the vessel, which remains in detention.
The arrests come after Iranian boats tried to seize a British oil tanker in the Gulf.
Three vessels, believed to belong to the Iranian Revolutionary Guard, approached the tanker while it was sailing through the Strait of Hormuz.
But British warship HMS Montrose, which reportedly had its 30mm deck guns trained on the boats, warned them off over radio.
A Ministry of Defense spokesman said: "HMS Montrose was forced to position herself between the Iranian vessels and British Heritage and issue verbal warnings to the Iranian vessels, which then turned away."
"We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region."
The Iranian Revolutionary Guard, which is thought to have been operating the patrol boats, denied the incident, saying if it had received orders to seize any ships it would have done so immediately.
This comes after Iranian President Hassan Rouhani said Britain would face "consequences" over the seizure of an Iranian tanker.
The Department for Transport this week raised its security level for British shipping sailing in Iranian waters to its highest level, level three, meaning an incident is considered to be imminent.
Vessels were advised to take enhanced security measures and to avoid transiting through Iranian waters if at all possible.
Foreign Secretary Jeremy Hunt described the developments as "very concerning" and said security in the region was kept under constant review.
"We are constantly monitoring security and constantly keeping under review the kind of security we need to keep British shipping safe," he said.
As well as the Montrose, the Navy has four mine countermeasure vessels and the Royal Fleet Auxiliary Cardigan Bay logistics ship in the region.
With typically between 15 and 30 British-flagged merchant ships in Gulf waters on any one day, providing individual escorts has been ruled out.