The Queen and David Cameron have led tributes to Baroness Thatcher, who has died aged 87 following a stroke.
A Buckingham Palace spokesperson said, "The Queen was sad to hear the news of the death of Baroness Thatcher. Her Majesty will be sending a private message of sympathy to the family."
Prime Minister David Cameron extended his sympathies on his official Twitter page, writing, "It was with great sadness that I learned of Lady Thatcher's death. We've lost a great leader, a great Prime Minister and a great Briton."
The Conservative leader is currently in Madrid, but it has been confirmed that he will return to London on Monday having cancelled planned talks in Paris.
His US counterpart Barack Obama released a touching statement in which he said the world had lost "one of the great champions of freedom and liberty".
The president added, "Here in America, many of us will never forget her standing shoulder to shoulder with President Reagan, reminding the world that we are not simply carried along by the currents of history—we can shape them with moral conviction, unyielding courage and iron will.
"Michelle and I send our thoughts to the Thatcher family and all the British people as we carry on the work to which she dedicated her life—free peoples standing together, determined to write our own destiny."
London Mayor Boris Johnson said he was "very sad" to hear of the death of Baroness Thatcher, writing, "Her memory will live long after the world has forgotten the grey suits of today's politics."
Meanwhile, stars including Lord Sugar and Geri Halliwell have also taken to Twitter to pay tribute to the 'Iron Lady'.
"Margaret Thatcher died today. A great lady, she changed the face of British politics, created opportunity for anyone to succeed in the UK. RIP," tweeted The Apprentice star.
Spice Girl Geri wrote, "Thinking of our 1st lady of girl power, Margaret Thatcher, a green grocer's daughter who taught me anything is possible…x."
Britain's Got Talent's Amanda Holden, also reacted the news, writing, "Whatever you thought about her. She shaped this country. RIP Margaret Thatcher."
Katherine Jenkins, meanwhile, recalled her own private moment with the former leader. "RIP Baroness Thatcher. I will always fondly remember the afternoon tea & chat at your home. #GirlPower."
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