The U.K. government plans to create a regulatory body to force the removal of harmful content from the internet, one of the most far-reaching legislative proposals from a host of countries trying to put a tighter leash on global technology companies.

The U.K. proposal, disclosed in a policy paper published early Monday, aims to create a new legal obligation for companies including Facebook Inc. and Alphabet Inc.’s Google to take “reasonable and proportionate” action on a gamut of illegal or potentially harmful content published on their platforms, ranging from terrorist propaganda to cyberbullying and disinformation.

The government said the new regulator would be armed with powers to enforce compliance, including potentially the power to issue civil fines for demonstrated failures in some areas.

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It said that issue would be refined in coming months through consultations on an eventual law.

The U.K.’s proposal comes amid renewed momentum from governments—from Australia and New Zealand to the European Union—to force companies to take more responsibility for the content they disseminate, from pirated music to extremist manifestos. Those calls have grown since allegations that Russia abused social-media tools to inject polarizing disinformation into the 2016 U.S. presidential election—and were amplified after last month’s terrorist attack in Christchurch, New Zealand, which the attacker broadcast live over Facebook.

The new proposals and laws represent a shift from an older model, where companies have often remained protected by generation-old rules that shield them from liability for content their users disseminate. Companies generally have signed on to voluntary measures to curb the spread of illicit content but increasingly face legal obligations, too.

Germany, for instance, last year implemented a law that threatens up to €50 million ($56 million) in fines for companies that systematically fail to remove hate speech.

“The era of self-regulation for online companies is over,” said Jeremy Wright, the U.K.’s digital secretary, in remarks accompanying the proposal rollout. In an interview with The Wall Street Journal on Monday, he said he hoped the move would be “a model that other countries, including the U.S., will want to look at very carefully.”

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He said the new regulator could impose sanctions within the scope of European fines already being levied against companies that breach the bloc’s new privacy rules. Such fines can run into the billions of dollars, though so far they have been much smaller. Mr. Wright said the government was also looking at holding individual company directors liable, as well as the possibility of blocking internet service providers.

Big tech companies say they already work hard to remove illicit and harmful content and increasingly use automated artificial-intelligence tools to do so. While tech executives increasingly say they also embrace regulation, TechUK, a lobby group for firms including Facebook, Google, Amazon.com Inc. and Apple Inc., said that the U.K. proposal would need to become more specific to avoid subjecting companies to uncertainty. “Not all of the legitimate concerns about online harms can be addressed through regulation,” the group said.

Facebook said that it supports new internet regulations, and plans to work with the U.K. government and Parliament to help shape the rules. But the company also raised what has often been a tense issue for tech companies facing content restrictions: how to balance the removal of potentially harmful postings with Silicon Valley’s more general embrace of free speech and enterprise.

Click here for more from The Wall Street Journal, where this story was first published.