Queen Elizabeth II dies

US President Joe Biden called the queen a "stateswoman of unmatched dignity and constancy who deepened the bedrock alliance between the United Kingdom and the United States."

European Commission President Ursula von der Leyen said she learned of the queen's death "with deep sadness", adding that she is "one of the most respected personalities worldwide".

Canada's Prime Minister Justin Trudeau praised the queen's "wisdom, compassion and warmth".

India's Prime Minister Narendra Modi said in a tweet: "She provided inspiring leadership to her nation and people. She personified dignity and decency in public life."

The queen has suffered from what the palace called "mobility issues" and reduced her appearance in public this year as she marked her Platinum Jubilee.

On Tuesday, she presided at a ceremony at Balmoral Castle to accept the formal resignation of Boris Johnson as prime minister and appoint Truss as his successor.

Earlier on Thursday, Buckingham Palace said in a news release that she was under medical supervision as doctors were concerned about her health. It was later reported that members of the royal family had traveled to Balmoral Castle in the afternoon, before her death was announced after 6 pm.

Agencies contributed to this story.