Image-heavy microblogging service Tumblr disappeared from Apple's App Store last week to the puzzlement of iPhone users, now the service has revealed child pornography is to blame.

Key points: Tumblr initially said it was working to resolve an issue with the App Store

Tumblr initially said it was working to resolve an issue with the App Store Three days later it issued a statement reiterating its anti-child-porn commitment

Three days later it issued a statement reiterating its anti-child-porn commitment Tumblr admitted some material had slipped through and they "immediately removed" what was found

The app was delisted from the store last week without a clear explanation, with Tumblr at the time saying they were "working to resolve an issue with the iOS app and hope to be fully functional again soon".

Similar updates were posted over the next two days, but this week a statement on their website seemed to acknowledge the App Store delisting was not a glitch, rather it was a move to try to stop the spread of exploitative content.

"We're committed to helping build a safe online environment for all users, and we have a zero-tolerance policy when it comes to media featuring child sexual exploitation and abuse," Tumblr's statement read.

Any trace of Tumblr seems to have been scrubbed from Apple's website. ( ABC News )

"As this is an industry-wide problem, we work collaboratively with our industry peers and partners like NCMEC [National Centre for Missing and Exploited Children] to actively monitor content uploaded to the platform."

The statement said Tumblr cross-checked every image uploaded with a database of known child sexual abuse material, which stops those images from ever reaching the platform.

But it also admitted there was some content live on Tumblr that had not been blocked by that process.

Tumblr is still available for Android users on Google Play. ( ABC News )

Tumblr said that content was "immediately removed", but gave no timeline for when the app would be relisted on the App Store.

"Content safeguards are a challenging aspect of operating scaled platforms," the statement read.

"We're continuously assessing further steps we can take to improve and there is no higher priority for our team."

Tumblr terminating questionable accounts

The service also appears to have started shutting down whole accounts for this sort of content.

One user who routinely posts pornographic cartoons was furious to discover his content account had been taken down because it violated the policies around "inappropriate content involving or depicting minors".

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"The termination is final and replies to this message are not reviewed," the Tumblr Trust and Safety message read.

"Guess nothing I have to say about this matters," tweeted the user, whose bio says he posts "very NSFW" (not safe for work) art.

Any references to the service appears to have been completely scrubbed from the App Store, with the store returning zero results when Tumblr is searched for.

As of now, it appears Android users are still able to download the microblogging app through Google Play.