More child sexual abuse imagery is being found on the internet than ever before, according to new research by a British charity which tracks such images online.
The Internet Watch Foundation found 78,589 URLs featuring disturbing content last year, a 37% rise on the previous 12 months.
Around a third of this content featured the most severe Category A abuse, which includes the rape and sexual torture of children.
Home Secretary Amber Rudd (pictured), in a foreword to the charity's annual report, said the threat faced by children and the generation and spread of online sexual abuse continues to grow.
She added: "I am encouraged that more of the public recognise child abuse material when they see it and are confident enough to report it, reflected in the statistics in this report.
"This demonstrates the success of the partnership between the Internet Watch Foundation and others, to encourage reporting this heinous material and to ultimately secure its removal.
"But there is clearly more that we need to do, with a worrying rise in material hosted in Europe, and the ever-evolving nature of offending as offenders exploit new vulnerabilities in the online environment to evade detection.
"We will continue to work together in our efforts to rise to this challenge and to evolve with it as we look to ensure the UK's response remains as strong as it can possibly be."
According to the charity's research, the most serious Category A images, depicting rape and sexual torture, rose to 33% from 28% of all content online last year. Category B images rose from 19% to 21%.
The Internet Watch Foundation also saw an increase of 86% in disguised websites, from 1,572 websites in 2016 to 2,909 in 2017.
These are websites where the child sexual abuse content is only revealed to someone who has followed a pre-set digital pathway.
To anyone else, they will only show legal content, which indicates an increased intelligence among a select number of offenders who are going to new lengths to evade detection.
Europe now accounts for 65% of all child sexual abuse imagery the charity sees, up from 60% last year.
It continues to be the worst continent for child sexual abuse material.
The top hosting countries of child sexual abuse URLs are the Netherlands, USA, Canada, France and Russia.
Overall, 87% of all child sexual abuse URLs identified globally in 2017 were hosted in just these top five countries.
Susie Hargreaves, chief executive of the Cambridge-based charity, said: "We are now receiving more reports of child sexual abuse content than ever before.
"This year we're seeing offenders getting smarter and finding new ways to abuse legitimate internet services. Our trends analysis tracks this development.
"It's concerning that offenders appear to be increasingly using concealed digital pathways to prevent law enforcement and hotlines around the world detecting these criminal websites.
"We are making huge technological advances, which we'll be announcing later in the year, but we also need to continue to work globally, in partnership, to fight this disturbing crime. This battle cannot be won in isolation."
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Peter Byrne / PA Wire.