A 23-year-old who ran one of the biggest ever dark web sites selling access to 250,000 images of child abuse has been charged in the US after a global inquiry sparked by UK investigators.

An indictment was unsealed against the site’s administrator Jong Woo Son, from South Korea, by US officials on Wednesday.

The site, Welcome To Video, was taken down in March 2018, and so far globally 337 suspected users have been arrested in 38 countries.

The site was uncovered by the National Crime Agency (NCA) during its investigation into one of the UK’s most prolific paedophiles Matthew Falder, who is serving 25 years in prison for 137 offences linked to the sexual abuse of children.

Dr Matthew Falder
Matthew Falder, one of the UK’s most prolific paedophiles, who used the Welcome to Video abuse site (NCA handout/PA)

The Cambridge graduate, now 30, blackmailed a series of victims and was branded “warped and sadistic” by the judge who jailed him.

Investigators tracked down the site operator to South Korea and analysed transactions in the cryptocurrency Bitcoin to identify site users.

Records suggested there were 1.3 million separate Bitcoin accounts, each a potential customer of the depraved site.

Among those, 18 UK-based users have been put under investigation, including seven men who have been convicted.

They include Kyle Fox, from Epsom in Surrey, who was jailed for 22 years in March this year for sexually abusing a five-year-old boy and a three-year-old girl and uploading images to the dark web site.

Kyle Fox court case
Kyle Fox abused two children and uploaded images to dark web site Welcome To Video (NCA handout/PA)

US officials said that to date, 23 child victims had been identified and rescued from their abusers.

NCA director of investigations Nikki Holland said: “Dark web child sex offenders – some of whom are the very worst offenders – cannot hide from law enforcement.

“They’re not as cloaked as they think they are, they’re not as safe as they think they are.

“The NCA is relentless in pursuing them and we have specialist capabilities, which we use for all UK law enforcement, to unmask them and help take down sites like Welcome To Video.

“I’m immensely proud of the role we played in catching some very depraved and dangerous global offenders and for beginning the work that eventually caught Jong Woo Son.”

Son is currently serving an 18-month jail term in his native South Korea.