The child protection charity the NSPCC has said it has been contacted about more than one "vile" Twitter accounts with "disturbing imaged of children."
It has said police are "taking urgent action":
People have expressed concern about a twitter feed with disturbing images of children. We've alerted CEOP. They are looking at it urgently.
Thanks all for raising concerns. We are aware there is more than 1 account. And we will of course be talking to twitter about this.
We share people's concerns about twitter today. Very disturbing. Police taking urgent action. And we will follow up with twitter.