IRAN said yesterday that the speed of its investigation into a British-flagged tanker depends on the cooperation of its crew, after ignoring calls to hand back the vessel.

The Stena Impero tanker was impounded with its 23 crew members on board at the port of Bandar Abbas after the Islamic Revolutionary Guard Corps seized it Friday.

The Guards on Saturday released video footage showing a ship with the Stena Impero’s markings being surrounded by speedboats before troops in balaclavas descend down a rope from a helicopter onto the vessel.

The Islamic republic has detained the oil tanker on allegations of failing to respond to distress calls and turning off its transponder after hitting a fishing boat.

Its crew is made up of 18 Indians, including the captain, three Russians, a Latvian and a Filipino.

“All of them are in full health, they are on the vessel and the vessel is anchored in a safe place,” said Allah-Morad Afifipoor, director-general of the Hormozgan province port and maritime authority.

“The investigation depends on the cooperation by the crew members on the vessel, and also our access to the evidence required for us to look into the matter.”

Britain told the United Nations Security Council on Saturday that the tanker seized by Iran was approached by Iranian forces when it was in Omani territorial waters and the action “constitutes illegal interference.”

Friday’s action in the global oil trade’s most important waterway has been viewed in the West as a major escalation after three months of confrontation that has already taken Iran and the United States to the brink of war.

It follows threats from Tehran to retaliate for Britain’s July 4 seizure of the Iranian tanker Grace 1, accused of violating sanctions on Syria.

British Foreign Secretary Jeremy Hunt said the incident showed “worrying signs Iran may be choosing a dangerous path of illegal and destabilizing behavior,” adding that the U.K.’s response would be “considered, but robust.”

The Foreign Office summoned the Iranian charge d’affaires Saturday afternoon. Meanwhile, the government was set to convene a second emergency meeting of national security officials to discuss its response, a Downing Street spokeswoman said.

The U.K. has warned ships connected to the country’s shipping industry to “stay out of the area.”

Iranian Foreign Minister Javad Zarif responded to Britain’s warnings Saturday with one of his own. “Unlike the piracy in the Strait of Gibraltar, our action in the Persian Gulf is to uphold intl. maritime rules,” Zarif said on Twitter. Observers had expected Iran to respond to the Grace 1’s seizure, and the U.K. raised the security level for British ships in the Persian Gulf just last week. (SD-Agencies)