Wreaths laid to honour the 52 victims of the 7/7 London bombings
Mr Khan was joined by the chief constable of British Transport Police Paul Crowther, Metropolitan Police commissioner Cressida Dick and City of London Police commissioner Ian Dyson to honour the 52 people killed in the bombings on July 7, 2005.
All of the bombers, who struck three Tube trains and a bus, had links to West Yorkshire.
"We will never forget those innocent victims, and as we grieve for them we also pay tribute to the heroic efforts of the emergency services and first responders who selflessly ran towards danger to help others.
"Londoners showed resilience and unity in the face of huge adversity in 2005, and sadly our city has faced difficult times since then.
"But, standing together, we uphold the values that make this the best city in the world, united in defiance against terrorism."
Home secretary Sajid Javid also paid his respects.
He tweeted: "We will never forget the 52 lives that were lost & the hundreds injured in the 7/7 attacks. Fourteen years on, our strength & resolve in the fight against terror remains undimmed. #WeStandTogether"
Mohammed Sidique Khan, 30, Shehzad Tanweer, 22, Hasib Hussain, 18 - who were all from Leeds and Dewsbury - and Jermaine Lindsay, 19, who previously lived in Dalton, Huddersfield, brought terror to London on July 7 2005.
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.