LONDON (Reuters Life!) - A third of teenage British girls say they have suffered sexual abuse at the hands of their boyfriends, according to a report by a children's charity on Tuesday.

A quarter of girls also experienced violence, the National Society for the Prevention of Cruelty to Children (NSPCC) said.

A survey by the NSPCC of more than 1,350 teenagers found that nine out of 10 girls aged 13 to 17 had been in an intimate relationship, with one in six of these saying they had been forced to have sex and one in 16 saying they had been raped.

"The high rate and harmful impact of violence in teenagers' intimate relationships, especially for girls, is appalling," said one of the report's authors, Professor David Berridge from the University of Bristol.

"It was shocking to find that exploitation and violence in relationships starts so young."

The report found that a quarter of girls had suffered physical violence such as being slapped, punched or beaten by their boyfriends.

Others said they had been forced to kiss or sexually touch.

A small number of boys also reported they had suffered pressure from girlfriends, with one in 17 in a relationship saying they had been forced into sexual activity and one in five suffering physical violence.

However girls reported they had suffered abuse more repeatedly and at a younger age.

"I only went out with him for a week," one of the girls interviewed for the study told researchers.

"And then because I didn't want to have sex, he just started picking on me and hitting me."

(Reporting by Michael Holden; Editing by Steve Addison)