LONDON (AP) — The British government says it will give regulators the power to fine social media companies for harmful material on their platforms.

Plans announced Wednesday would give the U.K.'s telecommunications watchdog, Ofcom, power to enforce a "duty of care" on companies such as Facebook and Twitter "to protect users from harmful and illegal terrorist and child abuse content."

Firms that allow harmful material to flourish or don't remove it quickly could be sanctioned. Ofcom currently keeps tabs on radio and television broadcasters, and has the power to levy fines or even kick repeat offenders off the air.

The government said it was "minded" to make the changes, but new legislation will be needed for it to take effect. It said officials were working "at pace" to draft a new law. Ofcom will hold companies to account if they don't deal with harmful material, and platforms will have to remove "illegal content" quickly and "minimize the risk of it appearing."

In order to safeguard freedom of expression, the rules won't ban people from accessing or posting offensive but legal content, though the government indicated it would let internet companies decide what material is tolerated.

Online companies "will be required to explicitly state what content and behaviour is acceptable on their sites in clear and accessible terms and conditions and enforce these effectively, consistently and transparently," the government said.

Tech companies welcomed the regulations.

"Facebook has long called for new regulations to set high standards across the internet," said Rebecca Stimson, the social network's head of U.K. public policy. "New rules are needed so that we have a more common approach across platforms and companies aren't making so many important decisions alone."

YouTube, owned by Google, said it looked forward to "working in partnership with the Government and Ofcom to ensure a free, open and safer internet that works for everyone."

Digital Secretary Nicky Morgan said the new rules would be "proportionate and strong."

"We have an incredible opportunity to lead the world in building a thriving digital economy, driven by groundbreaking technology, that is trusted by and protects everyone in the U.K.," she said.

The National Society for the Prevention of Cruelty to Children said it welcomed "a duty of care model that puts the onus on big tech to prevent online harms."

But free-speech advocates have expressed concerns about state attempts to limit activity that may be harmful but is not illegal.