X has blocked the European Commission from making adverts on its platform - a move which comes a few days after it fined Elon Musk's site €120m (£105m) over its blue tick badges.

Nikita Bier, who has a senior role at the social media site, accused the European Union (EU) regulator of trying to "take advantage" of "an exploit" in its advertising system to promote its post about the fine on Friday.

"It seems you believe that the rules should not apply to your account," he said. "Your ad account has been terminated."

A European Commission spokesperson told BBC News the Commission "always uses all social media platforms in good faith".

X's fine, issued on Friday, was the first under the EU's Digital Services Act.

The EU regulator said the platform's blue tick system was "deceptive" because the firm was not "meaningfully verifying users".

"This deception exposes users to scams, including impersonation frauds, as well as other forms of manipulation by malicious actors," it said.

It claimed X was also failing to provide transparency around its adverts, and was not giving researchers access to public data.

The social media platform has been given 60 days to respond to the Commission about concerns surrounding its blue checkmarks, or face extra penalties.

Following the fine, Elon Musk posted on his platform to say the EU "should be abolished", and retweeted a response from another X user comparing it to fascism.

US Secretary of State Marco Rubio and the Federal Communications Commission (FCC) accused the EU regulator of attacking and censoring US firms, adding, "the days of censoring Americans online are over".

'Never been abused like this'

The dispute originated with Mr Bier, who accused the Commission of activating a rarely-used account "to take advantage of an exploit".

He claimed it had posted a link which itself deceived users - tricking them into thinking it was a video "to artificially increase its reach".

He said the "exploit", which had "never been abused like this", had now been removed.

Ad accounts on X are used by businesses to create and analyse paid advertising campaigns and run "promoted" posts on the site, separate from the users' X profile.

In response, a European Commission spokesperson told BBC News that it was "simply using the tools that platforms themselves are making available to our corporate accounts".

"⁠We expect these tools to be fully in line with the platforms' own terms and conditions, as well as with our legislative framework," it said.

And it is not the first time there has been disagreement between X and global regulators.

In 2024, Brazil's Supreme Court lifted a ban on X after it agreed to pay 28 million reais ($5.1m; £3.8m), and blocked accounts accused of spreading misinformation.

The previous year, Australia's internet safety watchdog fined it A$610,000 ($386,000; £317,360) for failing to cooperate with a probe into anti-child abuse practices.