The freed sailors - five Indians, one Latvian and one Russian - had already left the Stena Impero, an Iranian Foreign Ministry spokesman told state television, the BBC reported September 4.
The Stena Impero tanker was at the port of Bandar Abbas after the Islamic Revolutionary Guard Corps seized it on July 19.
Iran detained the oil tanker on allegations of failing to respond to distress calls and turning off its transponder after hitting a fishing boat.
There were 18 Indian citizens, including the captain, as well as three Russian, a Latvian and a Filipino national on board. There is no information as to what will happen with the rest of the crew.
The Latvian Foreign Ministry earlier submitted a note to the Iranian Embassy in Stockholm calling on Iran to release the Latvian citizen.
The Latvian national, a man born in 1978, is the chief assistant of the ship's captain.
Later in the day the Latvian Ministry of Foreign Affairs confirmed the move, saying: "The Ministry of Foreign Affairs would like to announce that the citizen of Latvia has been released from the tanker Stena Impero along with part of its crew. The Ministry of Foreign Affairs welcomes the freeing of the Latvian citizen and is currently engaged in providing the necessary consular assistance to enable his departure from Iran. The Ministry of Foreign Affairs hopes that the situation will be fully resolved, and it calls on Iran to release the detained vessel and the rest of its crew."