Politicians are desperate to find long-term solutions to London's violence crisis among young people.

Among those invited to City Hall were the parents of murdered teenagers Kiyan Prince and James Smartt-Ford.

But Ray Lewis, deputy mayor for young people, warned that there was no "magic solution" to violent crime.

He said community leaders must tackle the roots of aggression by examining why young men and women are growing up angry and disengaged.

Mr Lewis added: "These horrific crimes devastate families and we need to all work together on the necessary ways to treat the profound contempt for society and lack of self-respect that has alarmingly developed in some of our young people."

Metropolitan Police Commissioner Sir Ian Blair revealed on Thursday that more than 4,000 people have been searched as part of a blitz on knife crime.

His officers are using metal detector arches and hand-held scanners in operations across the city aimed at getting knives off the streets.

On his election earlier this month, Mayor Boris Johnson said dealing with knife crime was one of his top priorities.

Kit Malthouse, deputy mayor for policing, said: "The long-term solutions to youth crime are complex and will require a wholesale cultural shift."