Three of Sweden's biggest newspapers announced measures Tuesday to prevent the comment forums of their websites being used as platforms for hate speech.

The need to moderate comments by anonymous Internet users became apparent after the twin attacks by Anders Behring Breivik that killed 77 people in Norway in July, said the editor of the Aftonbladet daily, Jan Helin.

"One cannot be unmoved by such an event," he said.

The Aftonbladet, which backs the Social Democrats and is run by Norwegian media group Schibsted, as well as the Liberal-backing Expressen tabloid will in future allow only comments from people who identify themselves via a Facebook or other Internet account.

The Liberal Dagens Nyheter (DN), for its part, has made it impossible to leave any comment on its site pending a similar solution to be put in place by mid-October.

"The ideal is free and open debate that requires no moderator. Regrettably, the reality is different and comment forums are exploited by a small group of people who use them to express racist opinions, among others," said Bjorn Hedensjo, who runds the DN website.

Not all welcomed the move.

"Everybody should be able to express their view... regardless of whether they are communist or nationalist," a commentator using the pseudonym Mjaa said in a chat organised on the Expressen website.

"Will this political move not allow less serious forums to become more important?" asked "Pastor Brutus".

The newspapers insisted they were not seeking to censor the Internet or to prevent anonymous comment.

Norwegian newspaper Verdens Gang introduced a similar system earlier this month, allowing only comments left by people via their Facebook accounts.

It has since admitted that the solution was not foolproof as not everyone subscribed to Facebook, and some used fake accounts.

The number of comments left on the Verdens Gang site had dropped by 10 to 15 percent since then, "but the tone of the debate has changed," Aftonbladet pointed out to justify its own decision.

Expressen and DN are owned by Bonnier, Sweden's biggest media and publishing group.