Twitter's new owner must abide by online content rules being developed by the European Union, the bloc has warned.

Brussels made the observation after Elon Musk's deal to acquire the social media network for $44 billion solidified, and as the world's richest man said he wants to remove limits on what people can say on the site.

The United Kingdom, which is also developing rules for online content aimed at protecting netizens from hate speech, offered a similar warning, with a government spokesman telling The Guardian that Twitter's 217 million users will continue to be protected.

"We are introducing new online safety laws to safeguard children, prevent abusive behavior and protect free speech," the spokesman said.

The UK will compel all technology companies that have UK users to comply with its laws or face large fines, and even the prospect of being blocked.

"Regardless of ownership, all social media platforms must be responsible," a spokesman for Prime Minister Boris Johnson was quoted by the BBC as saying.

Thierry Breton, the EU's commissioner for the internal market, tweeted that the bloc's newly agreed Digital Services Act, which comes into force in 2024, will ensure "free speech" is not distorted into hate speech.

"Any company operating in Europe needs to comply with our rules－regardless of their shareholding," Breton tweeted. "Mr Musk knows this well. He is familiar with European rules on automotive, and will quickly adapt to the Digital Services Act."

Breton explained to the Financial Times: "We are open but on our conditions. At least we know what to tell him: 'Elon, there are rules. You are welcome, but these are our rules. It's not your rules which will apply here.'"

Companies that breach the EU's Digital Services Act, or DSA, can be fined up to 6 percent of their global turnover.

The DSA requires platforms to block content that promotes terrorism, commercial scams, or that is racist or sexist.

Musk responded to the warnings by tweeting: "The extreme antibody reaction from those who fear free speech says it all." He later seemed to soften his tone by tweeting: "By 'free speech', I simply mean that which matches the law. I am against censorship that goes far beyond the law."

Jack Dorsey, Twitter's co-founder, backed Musk as "the singular solution I trust" in taking the company forward.

Ironically, Twitter's acceptance on Monday of Musk's offer to buy the company led to a difficult Tuesday for Musk's automaker Tesla, with $126 billion wiped off its value. Experts said investors seemed to be jittery about Musk possibly needing to sell Tesla shares in order to buy Twitter.

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