Iran on Friday accused the United Kingdom of committing an act of "maritime piracy" on behalf of the U.S. after British commandos seized an Iranian supertanker they said was carrying oil to Syria in violation of European Union sanctions.

In a statement, Iran's foreign ministry called the U.K.'s move an "illegal" and "destructive" act of aggression and demanded "the immediate release of the oil tanker, given that it has been seized at the request of the U.S., based on the information currently available."

Mohsen Rezai, a senior Islamic Revolutionary Guards Corps commander, said Friday that Iran should retaliate by seizing a British tanker if the U.K. does not release the Iranian vessel.

"If Britain does not release the Iranian oil tanker, it is the authorities' duty to seize a British oil tanker," Rezai tweeted. "Islamic Iran in its 40-year history has never initiated hostilities in any battles but has also never hesitated in responding to bullies."

The U.K.'s seizure of the Iranian tanker in waters east of Gibraltar on Thursday came amid heightened military tensions between Iran and the United States, sparked by President Donald Trump's violation of the nuclear accord last year and continued belligerent threats.

While many European nations expressed skepticism given the flimsy evidence, the U.K. joined the U.S. in accusing Iran of carrying out attacks on two oil tankers in the Gulf of Oman last month.

U.S. national security adviser John Bolton, who reportedly backed airstrikes on Iran that Trump abruptly called off last month, applauded British forces for seizing the Iranian tanker in a tweet on Thursday.

"Excellent news: U.K. has detained the supertanker Grace I laden with Iranian oil bound for Syria in violation of E.U. sanctions," Bolton said. "America and our allies will continue to prevent regimes in Tehran and Damascus from profiting off this illicit trade."

Excellent news: UK has detained the supertanker Grace I laden with Iranian oil bound for Syria in violation of EU sanctions. America & our allies will continue to prevent regimes in Tehran & Damascus from profiting off this illicit trade. — John Bolton (@AmbJohnBolton) July 4, 2019

According to the London-based Financial Times, British "Royal Marines boarded the Grace 1 from a naval helicopter and patrol boats in a joint operation with Gibraltar police" in the early hours of Thursday morning.

"[T]he UK seized the Grace 1 because it suspected that the vessel was violating European sanctions on Syria," according to FT.

Reporting from Tehran, Al Jazeera's Dorsa Jabbari said the Iranian government does not believe it is violating any international sanctions.

"They don't recognize the E.U. sanctions on the Syrian government as legitimate because they have not been endorsed by the United Nations," Jabbari said. "They say that this act by the British government on behalf of Americans is tantamount to piracy."

Matthew Oresman, a U.S.-based lawyer who advises firms on sanctions, told Al Jazeera that the seizure of the Iranian tanker was likely carried out in partnership with the Trump administration.

"This is the first time that the E.U. has done something so public and so aggressive," Oresman said. "I imagine it was also coordinated in some manner with the U.S. given that NATO member forces have been involved."