The storming of the British embassy in Tehran last month was not a planned attack but the result of an explosion of anger at London's meddling in Iranian affairs, a group that claimed responsibility for the incident said on Monday.
Three men who looked in their 20s said they were among the attackers of the British embassy compounds in Tehran on November 29 but expressed no remorse over their acts, which further increased Iran's international isolation.
Mostafa Mostajeran, one of the representatives of the so-called British spy nest pickets' council, said the intention had been to protest in front of the British mission and stage a 'mock arrest' of the ambassador.
There had been no prior planning made to enter the embassy. But the rage people felt towards Britain led to the loss of control and resulted in the entry into the embassy, he said.
The incident came after London announced new sanctions aimed at forcing Tehran to halt its nuclear activities. The European Union and United States are still discussing further sanctions that could hit Iran's vital oil exports.
Britain closed its embassy and evacuated all its staff after the attack, which it said could not have taken place without some degree of consent from the Iranian authorities. It hit back by shutting Iran's embassy in London and expelling the staff.
The incident brought Iran's relations with Europe to a new low, with France, Germany, Italy and the Netherlands withdrawing their ambassadors temporarily.
Witnesses said the British embassy buildings had been devastated in the attacks. Valuable paintings were slashed, personal belongings destroyed and offices set on fire.
British Foreign Secretary William Hague said the raids had been carried out by Basij militia, a voluntary force controlled by Iran's elite Revolutionary Guard.
The men at the news conference did not confirm or deny they were Basij members.
Don't refer to us as Basijis today ... What happened was merely a slap by revolutionary students, one of them, Mohammad Javad Nikravesh, told the news conference. He accused British stooges of inflicting some of the damage to harm Iran's image.
Nikravesh was seated next to a photograph of Majid Shahriyari, an Iranian nuclear scientist killed one year ago in a bomb attack Iran blames on Israel and its western allies.
Nikravesh said the protesters had found espionage and sedition documents on the British premises that they would pass on to Iranian intelligence.
Tension has been growing over Iran's nuclear programme, which Tehran says is purely for peaceful purposes but which the United States, Israel and leading Western countries suspect is aimed at building an atomic bomb.
Iran has warned it would retaliate against any Israeli or U.S. military strike in a way that would hurt U.S. troops in the region and disrupt the global economy.
A member of the Iranian parliament's National Security Committee said on Monday that the military was set to practise its ability to close the Gulf to shipping at the narrow Strait of Hormuz, the most important oil transit channel in the world, but a military spokesman declined to comment.
(Additional reporting by Hashem Kalantari; Writing by Robin Pomeroy and Parisa Hafezi; Editing by Mark Trevelyan)