Zarif also welcomed the fact that the "ordeal" of the tanker sought by the United States was over, adding that he hoped it would help reduce tensions.
The Adrian Darya 1, formerly the Grace 1, was captured on July 4 off Gibraltar over suspicions it was carrying Iranian oil to war-torn Syria in violation of EU sanctions, and subsequently became the subject of a diplomatic dispute.
The destination port is registered as Kalamata, and the supertanker is due to arrive there on Sunday, according to the website. It is not clear, however, if this is the vessel's final destination.
"Because of US sanctions, we cannot be very transparent with the destination of our oil," Zarif said, accusing the United States of attempting to "bully" clients.
The Supreme Court of Gibraltar - a British overseas territory - granted the tanker free passage last week despite a last-minute US request that the vessel continue to be detained.
Iran has insisted that the tanker is not going to deliver its oil to Syria, the Greek authorities said.
In Tehran, the release of the supertanker was seen as a great victory, observers said - not only against London, but especially against the US and President Donald Trump.
Subsequently, the Iranian Revolutionary Guards proved they have capacity to stop tankers in shipping lanes off Iran, as was the case in July when the British-flagged Stena Impero was seized in the strategically important Strait of Hormuz. Iran claimed that it had collided with a fishing ship and violated international law.
Haavisto, whose country holds the rotating European Union presidency, said he had raised concerns related to maritime security in the Strait of Hormuz and called for the release of the Stena Impoero and its crew during the meeting.
Zarif's visit to Helsinki also included a meeting with President Sauli Niinisto. He is later to visit Sweden and Norway.
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