A father spoke today of his 13-year-old daughter's terror as she was raped on a beach.

Two members of a four-man gang acted as lookouts while a third raped the victim.

The girl's father today offered a substantial reward for information leading to the conviction of the men responsible.

He told The Argus: "My daughter screamed and tried to fight off her attacker.

"She's deeply upset and won't leave the house now. She has been properly brought up and I'm not having this. I'm determined these people are caught and brought to justice." He said his daughter caught a bus to the Old Steine, Brighton, on Friday evening. Her attackers were on board.

He said: "She and her friend were going to the pictures but the friend change her mind and they went for a walk instead along the seafront."

The victim's friend left to go to the toilet.

The girl told her father it was then that the four men, two white and the others of Asian appearance and all about 19 or 20, surrounded her on the beach.

Police said the incident happened on a beach near the crazy golf pitch east of the Palace Pier at about 10pm or 10.15pm. She fled the beach and told a police community support officer in St James's Street she had been attacked.

Scores of seafront walkers were questioned, including many in the city for the weekend's speed trials, but police said no witnesses had been traced so far.

A spokeswoman said: "A thorough investigation is under way."

A man has been arrested but denies raping the girl.

Police searched the area and forensic experts scoured the beach for evidence. CCTV footage from the bus and city centre cameras was being checked.