A MASKED teenage robber threatened a 75-year-old woman with a knife as she walked her dog, a court heard.

The 15-year-old - wearing a skull-like mask based on one featured in the horror film Scream - tried to rob pensioner Gwyneth Jarrett on a riverbank near to Cwmbran, Cardiff crown court was told.

He lost his nerve and fled - but was arrested nearby, and police later found the mask and the knife in a bin.

Yesterday the youth was sentenced to three years' detention after admitting a charge of attempted robbery.

Judge Philip Richards told him: "The courts have been supportive of you in the past, but here you are again.

"This case is appropriate only for long-term detention. I feel very sorry for your parents and the victim.

"All she was doing was walking her dog.

"Elderly people ought to be able to walk their dogs in public areas without being subjected to what she was subjected to."

He said that wearing a mask the youth approached her, terrified her, and put a knife to her face.

"Your actions were designed to terrify her and you were motivated by greed.

"Your naked violence in a public place towards this vulnerable lady can be met only by the imposition of long- term detention."

Prosecutor Eugene Egan said Mrs Jarrett was walking her dog at about 11.45am on Friday, January 31.

She heard footsteps behind her, and as she turned the defendant put a hand on her shoulder. He was holding a knife with a six-inch blade.

He demanded money and she told him she had none, Mr Egan said, adding: "He brought the knife close to her face."

Mr Egan said the teenager - said to have previous convictions for arson and for affray - got "cold feet" and ran off.

He was arrested an hour later and gave "no comment" answers to all questions from the police.

Defence counsel Ieuan Rees said: "He is prepared to meet and apologise to his victim. He has personal difficulties and medical problems."