Children as young as seven are posting explicit images of themselves on the internet and allowing strangers to view them in sexual poses in their bedrooms via webcams, a “horrifying” new report has warned.

Egged on by adults viewing the pornographic material on websites, the youngsters are unaware that many of the images are falling into the hands of sex offenders, according to the Internet Watch Foundation (IWF), which conducted the study.

In just three months last autumn, researchers found nearly 4,000 photos or videos were posted of which 667 featured children aged 15 and younger and 286 depicted children believed to be 10 years old or younger. Girls featured in 93 percent of the images featuring children under the age of 15.

"This is one of the most shocking studies I've been involved in and we were very surprised at what we were seeing, because of the age of the children," said the report’s lead author, Sarah Smith.

One video described in the report showed a seven-year-old girl heavily made up and dressed in underwear lying on her bed and exposing herself to a webcam.

Leaning close to the camera she whispers: "Mum might see it and get worried and you know, like, delete my account."

Another video showed a 12-year-old girl using a webcam to get close-up footage of her urinating, before she told the person at the other end of the camera: "So, now we're officially boyfriend and girlfriend. Well, internet boyfriend and girlfriend as we may never actually get to kiss."

Smith said that the study was not able to establish exactly what motivated young children to take part in this sexual behaviour, but that in some instances they may have been abused and learned the behaviour.

In other cases she said they may have been trying to gain popularity on social media or they may have been bullied or blackmailed into taking part.

Appearing to demonstrate this, researchers found one video that showed a 10-year-old girl crying and "extremely distressed" and repeatedly shaking her head before eventually stripping naked for the camera.

"Comments made in relation to this video on the site on which it had been posted say this video is an example of a 'sextortion' video, whereby a child is blackmailed on the basis of sexual content they have shared with the blackmailer," the report states.

"If the child refuses to create more, the blackmailer will distribute the original content publicly."

Claire Lilley, head of child online safety at the NSPCC, warned that the children had no control over where the images would end up, adding that they could be shared "countless times" online.

"This is a horrifying situation for the young victims who will be scared and bewildered by what is happening," she said. "To protect them there must be more investment in crime enforcement agencies so they have the manpower and latest technology to prevent this hideous abuse."

However, a Home Office spokeswoman said the government was working with the industry and partners to block links that may lead to images of child abuse.