LONDON - A growing number of British teenagers are swapping sexually explicit images of themselves on mobile phones leaving them open to bullying and victimization by their peers, police and a children's charity said on Tuesday.

The practice, known as "sexting," has also resulted in intimate images of children being posted on websites used by paedophiles without the knowledge of the sender, according to Britain's Child Exploitation and Online Protection Center (CEOP).

"We are getting an increasing number of reports from the public, children and parents alike, who are concerned about this kind of behavior," said Helen Penn, head of education at CEOP, a law enforcement agency tied to the British police.

"We have seen an increase in children producing sexual images of themselves, and as a result we are seeing children's normal sexual exploration being translated into public property," she told Reuters.

Penn said advances in mobile phone technology, including Bluetooth, and the ability to post a picture or video on the internet at the click of a button, was making the practice more widespread with unforeseen consequences.

"If a relationship breaks down or someone finds that phone, then the image could end up on a website, a social networking site like Facebook, or could even end up in the wrong hands, as has happened, and end up on a pedophile network," Penn said.

A survey of 2,000 young people released by children's charity Beatbullying on Tuesday found that more than a third of 11 to 18-year-olds had received a sexually explicit text or email.

It also found that 70 percent of young people knew who had sent the message.

Chief executive of Beatbullying, Emma-Jane Cross, said it was important parents and schools understood the rise of the phenomenon, which was well documented in the United States and Australia, but comparatively unknown in Britain.

Girls were particularly vulnerable, the charity said, with evidence showing they were being bullied into taking and sharing intimate pictures by boyfriends.

CEOP's Penn said another key issue that had been overlooked is that children holding, or distributing indecent images of a person under 18 to someone else, could be breaking the law.

A survey of 70 young people aged 11 to 16 by CEOP's youth panel found that almost all of those questioned had no idea that holding on to the images or distributing them could be breaking the 2003 Sexual Offences Act.

"Obviously the law wasn't set up to prosecute children. It was set up to prosecute adults who were distributing this kind of image...but if they're (children) doing it maliciously, there are grounds perhaps to look at it as (a case of) harassment," Penn said.