The seven most popular far-right websites attract a total of 145,000 unique visitors a day, according to the report, which was prepared by the government-run Swedish Media Council and handed to the government on Tuesday.
"I'm surprised to find out that (the sites) have seven times more visitors than the total of all parties in parliament," Ulf Dahlquist, the council's research director, told Sveriges Radio (SR).
Three sites have more visitors each than all parliamentary parties combined, including realisten.se, run by the Neo-Nazi Party of the Swedes.
The report, which described websites advocating violence, did not give any figures for visits to the websites of political parties in parliament.
It noted that the extreme left did not enjoy a similar level of popularity, with the two top sites attracting a total of just 3,620 unique visitors a day. Islamist websites are even more marginalized with only about 500 unique visitors each day, according to the report.
Swedish European Affairs Minister Birgitta Ohlsson told SR the finding had to "be taken very seriously".
"You can never completely immunize a society against anti-democratic and extremist groups that favour violent action. But it's possible to take a large number of initiatives," she said.
Realisten.se denied advocating violence, arguing that the report ought to make the parties in parliament reflect on "their inability to set up popular websites."
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