Colonel Tim Collins, known for a pre-battle speech he made in Iraq, said Harry had now turned against his “other family, the military”.
Anas Haqqani, Taliban leader in Afghanistan, condemned the duke for describing those he killed as “chess players”, but added not many who killed Afghans “have your decency to reveal their conscience and confess to their war crimes”.
Lord Darroch, former national security adviser, said he “would have advised against” Harry revealing those details, while former commando Ben McBean told the prince to “shut up”.
It comes as the duke faces an intense backlash after writing about his time in Afghanistan in his controversial memoir, Spare.
Harry wrote that flying six missions during his second tour of duty on the front line in 2012 to 2013 resulted in “the taking of human lives”, of which he was neither proud nor ashamed.
The Telegraph, which obtained a Spanish language copy of the memoir from a bookshop in Spain, reported Harry said he did not think of those he killed as people, but instead as “chess pieces” that had been taken off the board.
“So, my number is 25,” he wrote. “It’s not a number that fills me with satisfaction, but nor does it embarrass me.”
But Col Collins criticised Harry for making the disclosure, calling it “a tragic money-making scam”.
He told Forces News on Friday: “Amongst his assertions is a claim that he killed 25 people in Afghanistan. That’s not how you behave in the Army; it’s not how we think.”
Col Collins later added: “Harry has now turned against the other family, the military, that once embraced him, having trashed his birth family.”
He also accused Harry of taking a path that is “alien” to those in the UK and the Commonwealth, adding the duke is “pursuing US identity politics and casting slurs or racism around where none exists”.
“I wonder whose path he has chosen? In the end I see only disappointment and misery in his pursuit of riches he does not need and his rejection of family and comradely love that he badly needs,” he said.
Mr Haqqani tweeted: “Mr. Harry! The ones you killed were not chess pieces, they were humans; they had families who were waiting for their return.
“Among the killers of Afghans, not many have your decency to reveal their conscience and confess to their war crimes.
“The truth is what you’ve said; our innocent people were chess pieces to your soldiers, military and political leaders. Still, you were defeated in that ‘game’ of white & black ‘square’.
“I don’t expect that the [International Criminal Court] will summon you or the human rights activists will condemn you, because they are deaf and blind for you. But hopefully these atrocities will be remembered in the history of humanity.”
Lord Darroch told Sky News he “slightly” shared the security concerns military experts have raised after Harry’s comments. “You have to respect all of those who fought in Afghanistan,” he said.
“I went there a number of times when I was national security adviser. It’s a really tough environment, it was a really dangerous war, we lost more than 500 British servicemen.
“I respect and appreciate all those who fought there. Personally if I’d been advising the prince, I would have advised against the kind of detail that he goes into there.
“But it’s out there now, and I believe it was a just war, and therefore what he has written about how he justified to himself what he was doing, I can understand and appreciate that.
“In terms of the detail, I personally wouldn’t have gone there, but it’s done now.”
Mr McBean, who lost an arm and a leg serving with the Royal Marines in Afghanistan in 2008, and was described by Harry as a “real hero” after they met at several events, tweeted: “Love you #PrinceHarry but you need to shut up! Makes you wonder the people he’s hanging around with.
“If it was good people, somebody by now would have told him to stop.”
A Ministry of Defence spokesman said they did not comment on operational details for “security reasons”.
Harry was criticised in early 2013 at the end of his tour when he disclosed that he had killed. The then 28-year-old told the media he took the enemy “out of the game” and soldiers “take a life to save a life”.
The Duke of Sussex has separately described how a “red mist” came over the Prince of Wales during his alleged physical assault, as the revelations from his memoir continued.
Harry has insisted he still wants reconciliation with the royal family, but warned there needed to be some accountability first. He shared more details with ITV’s Tom Bradby, in an interview to be broadcast in full on Sunday, about his claims William knocked him to the floor during a furious confrontation in 2019.
“I talk about the red mist that I had for so many years, and I saw this red mist in him,” Harry said. “He wanted me to hit him back, but I chose not to.”
In a clip from an interview with US show Good Morning America, Harry says his late mother Diana, Princess of Wales, would have been “sad” over her sons’ fractured relationship.
He also told CBS he was “probably bigoted” before he started dating his now-wife the Duchess of Sussex, and he was “incredibly naive” about how the British press would treat his relationship with the American mixed race actress.