TEHRAN: Iran's seizure of a British-flagged oil tanker in the Strait of Hormuz was a "legal measure", the spokesman for the Islamic republic's government said on Monday.

"Seizing the British tanker was a legal measure by Iran. Iran confronted the ship (to ensure) the region's security," Ali Rabiei told a news conference in Tehran.

Iran impounded the Stena Impero tanker on Friday on allegations it failed to respond to distress calls and turned off its transponder after hitting a fishing boat.

It has faced mounting calls to release the vessel and its crew -- 18 Indians, three Russians, a Latvian and a Filipino.

"To all the countries that are calling on Iran to release the tanker, we ask them to tell Britain the same thing," Rabiei said, referring to the seizure by the British authorities of an Iranian tanker in the Mediterranean on July 4.

"Comparing the two seizures is an unfair reading" of the situation, said the Iranian government spokesman.

"When you illegally seize the ship in Gibraltar, we too are not bound to tolerate any more," he said, while adding the seizure that Tehran carried out was not done in retaliation.

Iran said on Sunday that the fate of the Stena Impero depends on an investigation into its alleged breach of international maritime rules.

As well as failing to respond to distress calls and turning off its GPS tracker, it also says the tanker sailed in the wrong direction in the narrow waterway.

In a letter to the UN Security Council, London accused Tehran of "illegal interference".

It said there was no evidence of a collision and the vessel had been in Omani waters with its transponder switched on when it was approached. —AFP