Iran impounded the Stena Impero tanker on Friday on allegations it failed to respond to distress calls.

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.