Mayor of London Sadiq Khan has said the victims of the July 7 attacks will never be forgotten and recalled how the city's response "inspired the world".
Friday marks 12 years since 52 people died and hundreds were injured in attacks on the capital's transport system in the single worst terrorist atrocity on British soil.
Mr Khan said Londoners "always pull together", pointing out this has been evident again this year following the attacks in London Bridge, Westminster and Finsbury Park, as well as the tragedy of the Grenfell Tower fire.
He said: "Twelve years ago, our city suffered a cowardly and barbaric terrorist attack. Four co-ordinated suicide bombings across London's transport network killed 52 people and injured over 700.
"We will never forget those who lost their lives on 7/7 – and we honour them again today and they will always remain in our hearts.
"As well as grieving those we have lost, we also pay tribute to the heroic efforts of our emergency services and transport colleagues on that darkest of days.
"Our firefighters, paramedics, police and public transport staff fought to save lives in the most horrific and harrowing of circumstances. And our first responders showed tremendous bravery, running towards danger whilst directing others to safety.
"The way our city stood together in the aftermath of the 7/7 attacks inspired the world. When Londoners face adversity, we always pull together.
"We stand up for our values and our way of life. And we have shown this again during the difficult times our city has faced in recent months following the horrific terrorist attacks in Westminster, Finsbury Park and London Bridge, and the Grenfell Tower fire.
"The best way we can honour all those who tragically lost their lives is to ensure that we always stand together as a city, uphold our values and show the world that London will never be cowed by terrorism."
A wreath-laying ceremony will take place in London on Friday to mark 12 years since the bombings.
Suicide bombers Mohammed Sidique Khan, 30, Shehzad Tanweer, 22, Hasib Hussain, 18, and Jermaine Lindsay, 19, brought horror to London on July 7 2005.
Travelling from Luton, they took a train to King's Cross in London, hugged and separated to carry out the atrocities.
Within three minutes of 8.50am, Tanweer detonated his bomb at Aldgate, Khan set his device off at Edgware Road and Lindsay blew himself up between King's Cross and Russell Square. Hussain detonated his device on a bus at Tavistock Square at 9.47am.
Mr Khan's wreath had a note attached, which said: "We must never forget those who lost their lives on 7/7.
"We honour them again today and they will always remain in our hearts."
He was followed by London Fire Brigade Commissioner Dany Cotton, London Underground managing director Mark Wild, and London Ambulance Service chief executive Garrett Emmerson.
Representing the police were Metropolitan Police Commissioner Cressida Dick, City of London Police Commissioner Ian Dyson, and British Transport Police Chief Constable Paul Crowther, who saluted in unison after laying their wreaths.
Jennette Arnold, chairwoman of the London Assembly, and Peter John, deputy chairman of London Councils, also attended.