He again stressed that cycling in London is getting safer and that the fatal accidents should not lead to a reduction in cycling.
But the Green Party said his junction safety programme does not go far enough.
The mayor's comments came as he addressed a construction logistics and cyclist safety conference in London, an event arranged before last month's accidents.
Mr Johnson said that in the next few months Transport for London will be setting out a programme to make 33 junctions safer.
He said: "People go by bike because they love to go by bike.
"We must make cycling even safer and wherever accidents take place, we must respond. We must see what could have been done to prevent them, we must immediately work out what we can do to stop them happening again, and we must address people's fears, well-founded or otherwise."