Three of the world's biggest pornography sites are to face stricter regulation in the European Union.

Pornhub, Xvideos and Stripchat will be legally obliged to improve content moderation and toughen up age verification for users.

It is because they have been assessed as having at least 45 million monthly users in EU countries.

That means they are designated Very Large Online Platforms (VLOPs) under the EU's Digital Services Act (DSA).

EU Digital Commissioner Margrethe Vestager welcomed the companies' designation, saying it would "allow for higher scrutiny and accountability of their algorithms and processes".

"I have been very clear that creating a safer online environment for our children is an enforcement priority under the DSA," she added.

The BBC has approached Pornhub, Xvideos and Stripchat for comment.

The porn sites will have four months to ensure they meet a series of legal requirements including:

The EU Commission will be responsible for ensuring the sites meet the new, more stringent rules. It can fine them up to 6% of their global turnover if they fail to do so.

These companies are the second batch of firms to be designated VLOPs. In April, an initial 19 tech giants - including Facebook, Google and YouTube - were told the new rules applied to them.

For that initial round of companies, the DSA came into effect in August.

One of them, X (formerly Twitter), was told on Monday that the EU suspected it of breaking its obligation under the DSA to combat disinformation - the first enforcement proceedings to be launched under the legislation.