Queen Elizabeth has expressed her sadness at the passing of Baroness Thatcher.
Former British Prime Minister Margaret Thatcher died at home from a stroke on Monday morning, aged 87.
Her daughter, Carol Thatcher, said she had died peacefully, after a long battle with dementia.
A statement issued by Buckingham Palace read: "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."
Current Prime Minister David Cameron cut short a European tour to return to the UK after hearing the news.
He said in tribute: "It was with great sadness that l learned of Lady Thatcher's death. We've lost a great leader, a great prime minister and a great Briton."
Thatcher was the first female Prime Minister of Britain, taking office as a member of the Conservative party in 1979, and leading the country until 1990, when her leadership was challenged by Michael Heseltine, and she stepped down.
Out of respect for her passing, the Union Flags above Number 10 Downing Street and Parliament have been lowered to half-mast.
Thatcher's funeral will take place at London's St Paul's Cathedral and will have full military honours.