A total of 50 people in Florida, USA, were killed in the early hours of Sunday (June 12) after a terrorist entered a nightclub and gunned them down.
Islamic extremist group ISIS has claimed responsibility for the attack.
But, in an act of defiance, on Monday (June 13) Hammersmith and Fulham, Ealing and Hounslow councils raised a rainbow flag above their town halls, flown at half mast in respect for the victims.
The rainbow flag represents the LGBT community.
Ealing Council leader Cllr Julian Bell said: "The appalling atrocities in Orlando over the weekend have touched us all and our heartfelt condolences go out to the families and friends of the victims involved.
"Ealing is a vibrant and diverse borough with strong community cohesion and we will not tolerate discrimination.
"We are flying the Rainbow flag at half-mast in honour of those who have lost their lives and been injured by an act of senseless hatred, and to show our support for the annual Pride Festival this month".
Hounslow Council leader Steve Curran said: "We were all deeply shocked by the horrific shooting in Orlando, Florida, at the weekend.
"We are flying the Rainbow (Pride) flag at half-mast outside the Civic Centre, to show our solidarity with the LGBT community.
"On behalf of everyone at Hounslow Council, I send our sincere condolences to all the families and friends of the victims and all our thoughts and prayers are with the people of Orlando at this terrible time."