The tanker's detention "sets a unsafe precedent and must end now", Iran's Foreign Minister Mohammad Javad Zarif tweeted Monday.
Also Monday, Iranian Defense Minister Amir Hatami condemned Britain for seizing an oil tanker last week in Gibraltar on suspicion of carrying Iranian crude oil to Syria in violation of European Union sanctions. "We will not tolerate this kind of piracy by the United Kingdom".
The website reported the British energy giant is anxious about retaliation by Tehran after the Royal Marines seized an Iranian oil tanker entering the Mediterranean off the coast of Gibraltar last week.
Later on Monday, the government of Gibraltar said tests have shown the tanker was fully loaded with crude oil.
Iran's Foreign Ministry on Thursday summoned British ambassador to Tehran, Robert Macaire, over the issue of oil tanker seizure.
Britain should be "scared" about Tehran's possible retaliation for the capture of an Iranian supertanker by Royal Marines in Gibraltar, the Fars semi-official news agency on Saturday reported an Iranian cleric as saying.
Any country on the board can call a meeting, and the International Atomic Energy Agency confirmed in a note to member states that the meeting would be held next Wednesday at 2:30 pm after the IAEA this week said Iran had exceeded the maximum stock of enriched uranium allowed under the deal.
The tanker Grace 1 was stopped by Gibraltar authorities with the assistance of Royal Marines on July 4 in territorial waters that Spain claims fall within its jurisdiction.
The IAEA is in charge of verifying the restrictions on Iran's nuclear activities imposed by the deal, which also lifted worldwide sanctions against Tehran.