Boris Johnson will denounce the terrorists who killed nearly 3,000 people during the 9/11 attacks while paying tribute to their victims on the 20th anniversary.

The prime minister has recorded a video message that will be played at a memorial event on Saturday at the Olympic Park in east London where a memorial forged from the steel from Ground Zero – where the World Trade Center stood in New York – is on display.

In the message, he will say how September 11, 2001 “became, in President Roosevelt’s words after Pearl Harbour, a ‘date which will live in infamy'”.

Mr Johnson, who was born in New York City, will say how terrorists “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,” he will say.

“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.

“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.”

Mr Johnson will also congratulate Since 9/11, the organisation holding the memorial, for their “vital work to educate young people about what happened on that day”.

He will also mention the recent withdrawal of British and all foreign troops from Afghanistan nearly 20 years after sending troops there in reaction to the 9/11 attacks by Al Qaeda.

“Recent events in Afghanistan only strengthen our determination to remember those who were taken from us, cherish the survivors and those who still grieve and hold fast to our belief in liberty and democracy, which will always prevail over every foe,” Mr Johnson will conclude.

Labour leader Sir Keir Starmer has also paid tribute to those who lost their lives that day and say how the “consequences of the 9/11 attacks are still being felt to this day – the tragedy is still so raw”.

He said: “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.”