A family has moved out after youths stalked a 12-year-old girl and threatened to stab her.

It is the latest alarming example of a rising tide of yobbish behaviour afflicting towns and villages across Sussex.

The family fled its home in Warrior Close, Portslade, after one of the thugs threw a knife at the girl and, days later, made stabbing gestures at her in the street.

Mum Janet Clark said her daughter has become an emotional wreck after intimidation from the teenage boys she claims rule the area by threat of force.

She decided she had to take the girl and her other daughter, two, from the house because it is no longer safe.

Mrs Clarke, 33, has taken her family to live with her mother at her home nearby.

She said the gang has intermittently banged and thrown stones at the girl's ground floor bedroom window and shouted obscenities at her.

The trouble started about two years ago when the family was bombarded with disturbing notes posted through the letterbox. Her tormentors would send letters threatening to rape her in a campaign of abuse that lasted about seven months.

Threatening notes have been accompanied by tampons with abusive messages scrawled on them.

But in the last few weeks, Mrs Clark said, the intimidation had escalated and the yobs had started to threaten with knives.

Mrs Clark said: "I'm scared they're really going to hurt her.

"She no longer goes out or mixes and when she comes home she locks all the doors and closes the curtains because she's so terrified.

"One of them threw a knife at her which hit her foot.

"Twice she's seen him while riding on a bus and he's made gestures towards her as if he's going to stab her. On Tuesday she saw him on the street and he took out a kitchen knife. Apparently it's because we're born-again Christians but I don't see why we should be victimised for our beliefs." Community leaders said there were problems with antisocial behaviour which had to be tackled.

North Portslade Labour councillor Don Turner said he was "extremely concerned."

He said: "This isn't yobbish behaviour. This sounds criminal. I'm concerned to hear about this incident and clearly something needs to be done."

Police are investigating a string of incidents reported by Mrs Clark, who has also informed the William Sutton housing association.

Mrs Clark said people in the community are too scared to help with information.

She said: "Everyone's tried but William Sutton can't do anything and the police are struggling to."

The single mum was offered temporary bed and breakfast accommodation but is waiting to find out if she can be moved to a new home away from the trouble.

Letters urging Brighton and Hove City Council to find them another home have been sent by the family doctor, their church and the housing association.

Joe Chambers, regional director for William Sutton, said: "We've spoken with the youths, one of whom is already the subject of an acceptable behaviour agreement. If the case against him is proved we'll press for an antisocial behaviour order."

A police spokeswoman denied the area was a no-go area. She said: "There are some issues across the estate with small minded antisocial behaviour, and police and their partners are working closely to tackle the individuals involved."