Two teenage girls have pleaded guilty to a "happy slapping" attack, filmed on a mobile phone and broadcast over the internet.

Four children appeared at Mid Sussex Youth Court yesterday, charged with assault and harassment of a 15-year-old schoolgirl.

One girl, 16, who cannot be named for legal reasons, could be imprisoned after setting up a website showing footage of the playground attack.

Police said the site, dedicated to the intimidation of the young victim, had received more than 850 visits before officers shut it down.

Footage of the assault, which took place in February, was shown to magistrates, as well as print-outs of the website.

Prosecuting, Rachel Beckett said the site invited users to post messages ridiculing the victim as well as featuring distorted images of the schoolgirl.

Presiding, Geoff Oxlade told the two girls: "We are absolutely appalled by the content of this website. This is the worst such case we've ever seen."

Following the attack the victim heard about the website through friends and reported the incident to police.

She was also getting plagued by intimidating messages from one of the girls who used the "spiteful" website to get back at her after a falling-out, the court heard.

Mr Oxlade said the site, which was operational for more than two months, was "set up purely to harass" the victim and featured comments that were "grossly offensive" and "malicious".

The two girls, both 16, pleaded guilty to assault and harassment at the court in Haywards Heath.

After she admitted to punching the victim in the face during the attack in Mid Sussex, one was referred to a youth offending panel.

Magistrates said the other girl could receive a custodial sentence for her part in organising the website and have requested a pre-sentence report.

Two other teenagers, a 14-year-old boy and a 16-year-old girl, pleaded not guilty to the assault and will appear before magistrates again in October.