The Duke of Sussex has set out his manifesto for his public life, saying he and the duchess will "stand up for what we believe" and will use their position to help "build a better world".
Harry also said they would "seek to challenge injustice" - a comment likely to be interpreted as another justification of his decision to speak out about what he claims is a ruthless tabloid campaign against Meghan.
The duke's highly outspoken criticism of certain sections of the press on Tuesday night has overshadowed the couple's 10-day tour of Africa, which ends on Wednesday.
In the statement published on the duke and duchess's official website, Harry said he and Meghan believed in "media freedom and objective, truthful reporting" as a "cornerstone of democracy".
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Addressing readers, he added: "Unfortunately, my wife has become one of the latest victims of a British tabloid press that wages campaigns against individuals with no thought to the consequences - a ruthless campaign that has escalated over the past year, throughout her pregnancy and while raising our newborn son."
The couple looked relaxed when they arrived in a Johannesburg township to learn about an ambitious project, launched last year by South Africa's President Cyril Ramaphosa, which aims to tackle the critical issue of youth unemployment by creating one million new work opportunities in the next three years.
The duke and duchess's tour of Africa has received widespread and favourable coverage, but Harry said these positive publications expose the "double standards of this specific press pack".
Harry's strongly worded comments came with an announcement the duchess has launched legal action against the Mail on Sunday newspaper over an allegation it unlawfully published a letter to her father.
Speaking to a group of young people and fledgling entrepreneurs, Harry said: "Next year, we launch our new foundation and it's moments like today and meeting all of you that inspire us.
"Whether supporting young entrepreneurs, empowering women and girls or challenging the issue of gender-based violence, whether it be planting trees, clearing landmines or protecting the most beautiful creatures and places on this planet, these experiences have affirmed our love of Africa and the issues that are so important to us.
"We will firmly stand up for what we believe, we are fortunate enough to have a position that gives us amazing opportunities and we will do everything that we can to play our part in building a better world.
"We will also seek to challenge injustice and to speak out for those who may feel unheard. So no matter your background, your nationality, your age or gender, your sexuality, your physical ability, no matter your circumstance, or colour of your skin - we believe in you.
"And we intend to spend our entire lives making sure that you have the opportunity to succeed and change the world."
The couple were visiting a Youth Employment Services (YES) programme at a community hub, in the Johannesburg township of Tembisa, supported by British aid and the Foreign and Commonwealth office.
They saw local students from the township learn digital skills, met chef Mishak Masipa, 28, and saw a polytunnel where gardeners were growing organic lettuces to be sold locally.
During his open-air speech made at the end of the visit, Harry talked, with Meghan beside him, about how important Africa was to him when his father, the Prince of Wales, brought him to the continent following the death of his mother, Diana, Princess of Wales, in 1997.
He said: "Ever since I came to this country as a young boy, trying to cope with something I could never possibly describe, Africa has held me in an embrace that I will never forget and I feel incredibly fortunate for that.
"And every time I come here I know that I'm not alone. I always feel wherever I am on this continent that the community around me provides a life that is enriching and is rooted in the simplest things - connection, connection with others and the natural environment.
"And as I raise my own son, I'm going to make sure that what I've learnt here - the value of the natural world, the value of community and friendship - is something that I can pass on to him."
Meghan gave an impromptu speech and described how the couple had "loved" their visit to South Africa.
She said: "So, thank you for giving us the opportunity to meet with all of you, to be able to feel inspired and for welcoming us so warmly, strongly, beautifully to your country, we've loved it. Thank you."
Royal couple impressed by sanitary towel initiative
During their visit, the couple chatted to women from Blossom Care, a local business that makes 80,000 sanitary towels a month - all fully compostable after 90 days in the ground.
Meghan was particularly taken with the business - and excitedly showed her husband the manufacturing process in a portable cabin.
Meghan told the Blossom Care women: "I love it. I can't wait to see what's going on inside."
In her speech, made without notes, she said: "You really have been such an inspiration for us and being here today, from every level of what we've seen, there is such a holistic approach to how you have energised and mobilised each other to be part of a bigger change.
"And on a personal note, seeing the work that's being done at Blossom is incredible."
Yvonne Sibayoni, 27, and Portia Tivane, 32, were both unemployed before joining Blossom Care Solutions in June and met the duke and duchess during their visit.
Ms Tivane said about the royal visit: "That shows they care about people, not just in their country but in Africa as a whole.
"His speech was powerful, empowering young people, young women, young business. It was powerful that they will also donate money here. It's good for the community, especially Tembisa."
Tashmia Ismail-Saville, chief executive officer of YES, said: "One of the things they were so impressed with was the potential of the young people they met.
"Looking at the unemployment issues... that empathy meant a lot to the people there. When they engage with people, they really feel that they're in the conversation.
"We've trained over 3,500 people here and now have a 22-person classroom to train digitally which will help amplify our coding and design programmes."
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