Condoleezza Rice, who served as US secretary of state between 2005 and 2009, said she was "honoured to know and to be inspired" by Margaret Thatcher.
I am deeply saddened by the news of the passing of Baroness Thatcher.
There was no more potent force in the defense of freedom than this remarkable woman.
Her unshakable belief in the universal appeal of liberty helped to steer the free world through treacherous times until communism was defeated and Europe emerged whole, free and a peace.
I was honored to know her and to be inspired by her. Baroness Thatcher will be missed but generations will draw strength from the memory of her passion for freedom.
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Princess Charlotte is being christened on Sunday at Sandringham in Norfolk in only her second public appearance since she was born.