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
Nabi Tajima, who was the last known person to have been born in the 19th century, died in Japan after being in hospital since January.
Temperatures are predicted to reach a high of 23C.
Hunt accused companies of "turning a blind eye" to a generation of children "exposed to harmful emotional side effects" of social media.