"Having failed to accomplish its objectives through its #EconomicTerrorism - including depriving cancer patients of medicine - the US attempted to abuse the legal system to steal our property on the high seas," Foreign Minister Mohammad Javad Zarif said on Twitter on Thursday, Efe news reported.
"This piracy attempt is indicative of (the US government's) contempt for the law," he added.
Grace 1 was seized on July 4 by Gibraltar authorities - with help from the British Royal Marines - on suspicion it was transporting crude oil to Syria in violation of European Union sanctions against that country's government.
Iran, for its part, denied the tanker was bound for Syria and characterized its seizure as an act of piracy.
It was released on Thursday by order of a court in Gibraltar, a British overseas territory on the southern tip of Spain, after Iran provided assurances that the tanker's cargo would not be taken to Syria.
The vessel, which was carrying 2.1 million barrels of crude oil, was freed despite an effort by the US Justice Department to keep it detained.
In that regard, Iran's ambassador to the United Kingdom, Hamid Baeidinejad, said the US tried up to the last minute to prevent the release of the tanker but ended up suffering a "humiliating defeat."
Two days ago, the Ports and Maritime Organization of Iran had said the UK soon would release the tanker after an exchange of certain documents.
In apparent retaliation for the seizure of the Grace 1, Iran's Islamic Revolutionary Guard Corps on July 19 captured the British-flagged oil tanker Stena Impero in the Strait of Hormuz for allegedly violating international maritime rules, an accusation that London and the ship's owner have denied.
The Stena Impero was en route from the United Arab Emirates to Saudi Arabia with a 23-person crew when it was intercepted.
Iranian authorities are expected to release the Stena Impero shortly, considering they previously had floated the idea of a tanker exchange.
Those incidents have further heightened tensions in the Persian Gulf region, the scene since May of attacks on oil tankers that Washington has blamed on Iran and the June 19 shoot-down of a US surveillance drone that Tehran says violated its airspace, though the Pentagon said the aircraft was flying over international waters.
On July 18, US President Donald Trump said that a US Navy ship shot down an Iranian drone, although Iran denied having lost an unmanned aircraft.
The US has called for an international naval coalition to be formed to escort commercial vessels in the Strait of Hormuz, which connects the Persian Gulf with the Gulf of Oman and is a major crude oil shipping corridor.
Iran, however, said that Persian Gulf nations are capable of guaranteeing security in the region and that the formation of a maritime coalition force would increase the possibility of conflict.
Tensions between Iran and the US have sharply increased as a result of the Trump administration's move in May of last year to pull out of a 2015 multilateral pact under which Tehran accepted limits on its nuclear power program in return for relief from economic sanctions.
Washington, which said in pulling out of the accord that it was too lenient on Iran, has since imposed increasingly severe sanctions with the proclaimed intent of crushing the Iranian economy.
( With inputs from IANS )