THE Queen has said the "thoughts and prayers" of the Royal Family are with the victims of the 9/11 attacks in a touching post to Joe Biden.
On the 20th anniversary of America's darkest day, the 95-year-old monarch paid tribute to the victims, survivors, first responders and rescue workers in a heartfelt message to the US president.
The Queen said: "As we mark the 20th anniversary of the terrible attacks on September 11, 2001, my thoughts and prayers - and those of my family and entire nation - remain with the victims, survivors and families affected, as well as the first responders and rescue workers called to duty.
"My visit to the site of the World Trade Centre in 2010 is held fast in my memory.
"It reminds me that as we honour those from many nations, faiths and backgrounds who lost their lives, we also pay tribute to the resilience and determinations of the communities who joined together to rebuild."
A special changing of the guard ceremony during took place at Windsor Castle on Saturday to mark the anniversary of the atrocity.
Hundreds of people gathered inside and outside the walls of the castle as the US national anthem was played before a minute's silence was held.
The anthem was played at Buckingham Palace 20 years ago in solidarity with the victims of the terror attacks.
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Boris Johnson and Sir Keir Starmer have marked the anniversary by praising the "international resolve" which has grown from the al-Qaeda-led tragedy two decades ago.
In a defiant message to be played a memorial event at the Olympic Park in east London today, the PM said the threat of terrorism remained - but people refused to live their lives in "permanent fear".
"Twenty years ago, September 11, 2001 became, in President Roosevelt's words after Pearl Harbour, a 'date which will live in infamy'," he said.
"On a crystal clear morning, terrorists attacked the United States with the simple goal of killing or maiming as many human beings as possible, and by inflicting such bloodshed in the world's greatest democracy, they tried to destroy the faith of free peoples everywhere in the open societies which terrorists despise and which we cherish.
"And it is precisely because of the openness and tolerance of the United States that people of almost every nationality and religion were among the 2,977 murdered on that day, including 67 Britons, each of them a symbol of the eternal friendship between the United Kingdom and the United States.
"But while the terrorists imposed their burden of grief and suffering, and while the threat persists today, we can now say with the perspective of 20 years that they failed to shake our belief in freedom and democracy.
"They failed to drive our nations apart, or cause us to abandon our values, or to live in permanent fear."
My thoughts and prayers - and those of my family and entire nation - remain with the victims, survivors and families affected, as well as the first responders and rescue workers called to duty.
The Queen
The PM added: "The fact that we are coming together today - in sorrow but also in faith and resolve - demonstrates the failure of terrorism and the strength of the bonds between us."
Labour leader Sir Keir said the impact of the horror attacks were "still being felt to this day" - adding the tragedy was "still so raw".
He said: "20 years ago today the world was in shock as we witnessed an unprecedented and despicable act of violence on US soil.
"9/11 saw the deadliest terrorist attack in history... with almost 3,000 people tragically murdered... including 67 people from the UK. Today we remember and honour them.
"We show support to our American friends as they mark this difficult time in their history. And we remember those in all corners of the world who have lost their lives to terror.
"They will always be in our hearts and our memories. The consequences of the 9/11 attacks are still being felt to this day. The tragedy is still so raw.
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"But as we mark this anniversary I'm convinced our resolve has never been stronger.
"We will continue to fight terror and violence, by promoting our values of justice and peace."