Britain’s Prince Harry admitted that he killed 25 people during his time on duty as an Apache helicopter pilot in Afghanistan, reported the media on Thursday, quoting his much-awaited and soon-to-be-published autobiography.

The 38-year-old Duke of Sussex served two duty tours against the Taliban, first as a forward air-controller calling for airstrikes in 2007-2008, then flying the attack helicopter in 2012-2013.

In the book "Spare," due for release next week, he said he undertook six missions as a pilot that led to him "taking human lives," reported the Daily Telegraph.

He said he was neither proud nor ashamed of doing so and described eliminating the targets as like removing "chess pieces" from a board.

Harry served in the British Army for 10 years, rising to the rank of captain, and has described his time in the military as his formative years. His first tour was conducted under a strict news blackout for security reasons, which was agreed to by British media outlets. He was forced to return home when a foreign publication broke the embargo.

He has never publicly discussed how many Taliban combatants he killed. Video cameras mounted on the nose of his Apache helicopter enabled him to assess his missions – and determine with certainty how many he had killed. "My count is 25. It's not a number that fills me with satisfaction, but nor does it embarrass me," he wrote.

He justified his actions because of his memory of the 9/11 attacks in the United States, and his subsequent meeting with the families of victims. Those responsible and their sympathizers were "enemies of humanity" and fighting them was an act of vengeance for a crime against humanity, he added.

Harry has since voiced concern about his security, not just because of his royal status but also because of his time fighting abroad. The Telegraph quoted extracts from the Spanish version of the autobiography it obtained, after mistakenly being put on sale in bookshops on Thursday before being withdrawn.