LONDON (AP) — British Prime Minister David Cameron says he wants Internet service providers to automatically block access to pornography sites unless customers opt in.

Cameron is proposing the move as part of measures to stop extreme sexual images he says are "corroding childhood."

He said Monday "family-friendly" filters would become the default setting for new customers by the end of the year, and only account-holders would be able to change them.

He also announced a proposal to make it a crime to possess violent pornography containing simulated rape scenes, and said Google and other search engines would be asked to block searches based on certain phrases.

Anti-pornography activists welcomed the announcement, but Padraig Reidy of free-speech group Index on Censorship said it amounted to "a kind of default censorship."