Gordon Brown has promised "intensive" action to tackle gang violence involving guns and knives.
The prime minister said there would be "tougher enforcement" of the law in areas with a gang violence problem.
He also promised to get more police on the streets and to "crack down" on illegal sales of alcohol to under-18s.
His comments came after the arrest of two teenagers on suspicion of the murder of 11-year-old Rhys Jones in Liverpool, on Wednesday.
Mr Brown called the killing a "heinous crime" which had "shocked the country", adding that the "first responsibility is to track down those who are responsible".
He said most young people were "law-abiding" but added: "Where there's a need for early intervention, we will work very intensively with those families so that young people are deterred from going into gangs and guns and knife crime."
Mr Brown said: "Where there is a need for new laws we will pass them. Where there is a need for tougher enforcement we will make sure that happens."
'Nip in the bud'
The prime minister held a Downing Street meeting with Home Secretary Jacqui Smith to discuss how to tackle gang violence.
Ms Smith said number of acceptable behaviour contracts (ABCs) would be increased to up to four times the 25,000 currently in place.
This would help "nip in the bud" the disorder "which blights people's lives in communities", she added.
The government has issued guidance to police and local authorities on how to use ABCs - written pledges to improve behaviour - effectively.
The contracts - which last for six months - and involve an acknowledgment from the individual that their behaviour is having a negative impact on a community and an agreement to stop the behaviour.
They can also involve pledges to complete positive activities such as attending school or drug misuse support groups.
Mike Goodwin, the Association of Chief Police Officers' lead member on anti-social behaviour, said ABCs had proved effective.
He said: "Police, working together with local authority and youth justice partners have found that, in many cases where ABCs have been issued, offending will stop without recourse to legal remedies.
"This is great news for local people whose lives are blighted by anti-social or inconsiderate behaviour."
Ms Smith said the government was also investigating the link between cut-price alcohol and anti-social behaviour.
She told BBC Radio 4's Today programme: "There are two issues here. One: We do need to know whether or not price and promotion is impacting on alcohol misuse.
"Two: We need to stop young people from getting hold of drink.
"We have had some success already in tackling those, frankly dodgy, off-licences selling kids drink."
On Wednesday, Conservative leader David Cameron unveiled his strategy for combating anti-social behaviour.
Mr Cameron called for a "three-dimensional approach" focusing on strengthening families, freeing police from red tape and giving the courts more powers.
He also suggested young offenders could be barred from obtaining or holding a driving licence.
Liberal Democrat leader Sir Menzies Campbell called for a "change of atmosphere" in communities with gang violence, but said there was "no simple solution".
There was a feeling of "alienation" among some young people, he added.