Hardcore pornography was tweeted from an official government Twitter account.
The UK Government in Wales Twitter account shared the extremely graphic screenshot on Monday before it was quickly deleted.
A spokesman has since alleged that the account had been the victim of a "cyber-attack", according to WalesOnline.
The account has more than 14,000 followers. Its Twitter bio describes itself as "the face of the UK Government in Wales and the voice of Wales in Whitehall."
Stace Williams Tweeted: "That awkward moment when the UK Government in Wales account tweets porn into your timeline."
Another social media user posted: "Biggest faux pas of the day goes to whomever is running the UK Government in Wales @UKGovWales Twitter account who r/ted this."
Following the incident, UK Government in Wales posted on Twitter: "We are aware that our account was subject to a cyber-attack earlier.
"We apologise for any offence caused by the material shared.
"We are confident the issue has now been resolved.
"If you find yourself in a similar situation please see: https://ncsc.gov.uk/section/information-for/individuals-families."
