Prince Harry has been accused by Iran of committing a "war crime" after he admitted killing 25 Taliban fighters whom he likened to "chess pieces" in his book.
The regime also said that the UK was in "no position to preach" on human rights as it was "turning a blind eye" to Harry's revelations.
In a series of posts on Twitter, the Iranian foreign ministry criticised Britain's anger over the execution of a British-Iranian dual national accused of spying by Tehran.
"The British regime, whose royal family member, sees the killing of 25 innocent people as removal of chess pieces and has no regrets over the issue, and those who turn a blind eye to this war crime, are in no position to preach others on human rights," a tweet read.
The foreign ministry also said the UK government's outrage following the killing of former deputy defence minister Alireza Akbari was "a sign of their evasion and violation of law".
It added: "Britain's encroachment on the national security of the Islamic Republic of Iran has been met with a decisive response from the Iranian intelligence and judiciary."
He said he was neither "satisfied" or "embarrassed" by the death toll.
Harry wrote: "They were chess pieces taken off the board, bad guys eliminated before they kill good guys. They trained me to 'other' them and they trained me well."
Tory MP Tobias Ellwood suggested last week that the admission could create security risks.
Mr Ellwood, a senior backbencher and chairman of the Commons Defence Committee, said the revelation in Harry's memoir was "ill-advised".
"I do worry that this is going to have security implications," Mr Ellwood told Sky News.
Speaking about the Invictus Games, he said: "One of the rare occasions that I worked with Prince Harry was in the Invictus Games in Sydney and in Toronto and so forth. Incredible effort. This was his design, this was his creation.
"And I'm now concerned that something which has been so important to veterans to help rehabilitation will now suffer because there could be security implications of him participating in that."
Hameedullah Hameedi, a member of the provincial council in Helmand, Afghanistan, told Sky News: "If Harry considered himself a member of a civilised world, this is a shame for him to say that (he killed 25 people).
"And it is an even bigger shame for him to talk about it proudly, like an illiterate person of a poor society with no knowledge and no education.
"We are not only demanding that he be prosecuted in the international court, but also demanding the international community punish him as soon as possible."
The duke carried out two tours in Afghanistan during his time in the army, including one tour between 2012 and 2013 during which he served as an Apache attack helicopter co-pilot gunner.
Spare has sold 750,000 across all formats - hardback, audio and e-book - in the UK since its publication on 10 January and was recently announced as the fastest-selling non-fiction book ever.
Larry Finlay, managing director of Transworld Penguin Random House, said: "We announced last week that Spare was the fastest-selling non-fiction book ever on its first day of publication, a record that has been confirmed by Guinness World Records.
"We now know that it is also the biggest-selling memoir ever in its first week of publication."