Former US President Jimmy Carter said in a statement: "Rosalynn and I are deeply saddened to learn of the death of Margaret Thatcher. A principled leader, she was a strong ally for peace and human rights during my presidency.
"As prime minister, her government was in the forefront of those who stood with the United States on key concerns, including the need for the SALT treaty, a stronger NATO alliance, majority rule in Zimbabwe-Rhodesia, and efforts to bring the Iran hostages home peacefully.
"We extend our condolences to her family and the people of Great Britain on their loss."
More top news
President Barack Obama and First Lady Michelle Obama have celebrated Star Wars Day by getting down with R2-D2 and some storm troopers.
Police are appealing for information about two sisters aged 12 and five who went missing three days ago.
Senior medical staff have urged junior doctors and the Government to break the deadlock over the medics' long-running contract dispute.