What you need to know:
- Irish prime minister Enda Kenny paid tribute to the "gift" of Mandela, and offered the country's deepest sympathies to the people of South Africa.
British Prime Minister David Cameron on Thursday said "a great light had gone out" following Nelson Mandela's death, revealing that flags would be flown at half-mast at his Downing Street Office.
"A great light has gone out in the world," said a statement released by Cameron.
"Nelson Mandela was a towering figure in our time; a legend in life and now in death -- a true global hero.
"Across the country he loved they will be mourning a man who was the embodiment of grace," he added.
"Meeting him was one of the great honours of my life. My heart goes out to his family - and to all in South Africa and around the world whose lives were changed through his courage.
"I've asked for the flag at No.10 to be flown at half mast."
Opposition leader Ed Miliband said the world "had lost the global hero of our age".
"Nelson Mandela showed us the true meaning of courage, hope, and reconciliation," he wrote on Twitter.
Shadow finance minister Ed Balls also took to the blogging site, writing: "Seeing Nelson Mandela walking free is one of the great moments of my life - proving leadership and hope can triumph. Thank-you. RIP"
Irish prime minister Enda Kenny paid tribute to the "gift" of Mandela, and offered the country's deepest sympathies to the people of South Africa.
"The name Mandela stirred our conscience and our hearts. It became synonymous with the pursuit of dignity and freedom across the globe," he said in a statement.
"As we mark his passing, we give thanks for the gift of Nelson Mandela. We ask that his spirit continues to inspire, guide and enlighten us as we strive to bring freedom and dignity to the family of man, our brothers and sisters, across the world," he added.