Gibraltar said on Friday it had obtained an order extending the detention of the Iranian Grace I supertanker by 14 days because there were grounds to believe it was breaking sanctions by taking oil to Syria.
Earlier the Spanish government said it planned to lodge a formal complaint over the British military’s seizure ofthe tanker.
"We are studying the circumstances and looking at how this affects our sovereignty," Josep Borell, Spain's acting foreign minister, said. Spain considers the sea around Gibraltar to be part of its international waters, while the British regard it as theirs.
According to official reports, British authorities notified Spain that the ship was about to be boarded by Royal Marines on Thursday night and the entire operation was closely watched by a civil guard patrol boat.
"Spain didn't want to interfere because the issue was compliance with European Union sanctions," a Spanish foreign ministry spokesman said.
Fabian Picardo, Gibraltar's chief minister, said the tanker was believed to be en route to the Banyas refinery which "is the property of an entity that is subject to EU sanctions against Syria".
The complaint derives from the fact that the ship, Grace 1, was seized on the open sea and not in the port of Gibraltar.
Mr Borrell also contradicted the British claim that the marines were under the command of the Gibraltar police, alleging that they were acting under US orders.
An Iranian Revolutionary Guards commander on Friday threatened to seize a British ship in retaliation. "If Britain does not release the Iranian oil tanker, it is the authorities duty to seize a British oil tanker," Mohsen Rezai said on Twitter.
A British diplomatic source told El Pais newspaper they believed Spain and the UK were working together to ensure the sanctions were complied with.
“There is no doubt that the Spanish government also supports the sanctions despite the fact that both governments have unfinished business concerning the territorial dispute over Gibraltar,” the source said.
The action comes at a time of heightened tensions between the US and Iran. Washington has accused Tehran of sabotaging oil tankers in the strait of Hormuz.
The ship’s seizure has created a diplomatically delicate situation for the UK as it strives to maintain good relations with Iran. The British ambassador to Tehran was summoned to the foreign ministry to account for what Iran said was an illegal seizure.
It is understood Rob Macaire told the Iranians that he and the British government supported the action by the Gibraltarian authorities to enforce sanctions against the Syrian regime of Bashar al-Assad.
The 28 members of the ship’s crew were questioned on board by Gibraltarian authorities. They were mostly Indian nationals as well as some Ukrainians and Pakistanis, the territory’s government said.
Mr Picardo thanked the efforts of the “brave men and women” from the marines and the local agencies involved in the operation. – Guardian/Reuters