Home Secretary Sajid Javid also waded into the debate over her legal aid, saying he understands people's concerns.
Some of the names of those killed were read aloud at London Central Mosque, before those present bowed their heads for a minute of silence.
The home secretary argued that increased police numbers alone would not solve the problem.
A string of fatal teen stabbings have sparked a heated debate over police officer numbers in England and Wales.
Mrs May, a former home secretary, insisted there was "no direct correlation between certain crimes and police numbers".