A study of extremist groups in Sweden finds that Islamic extremists pose the biggest threat of terrorist violence.

The study looked at extremists on the far left and far right, but finds that an election year there, and a possible return of Swedes who have joined the Syrian jihad, increase the potential for violence. Sweden's national police agency, Säpo, reported that at least 75 Swedes have gone to Syria to join the fight against dictator Bashar al-Assad.

The report was presented Friday to Democracy Minister Birgitta Ohlsson.

The country saw its first suicide bombing in 2010, carried out by a man who moved to Sweden as a child but reportedly became radicalized during his college years in England.

Sweden is home to cartoonist Lars Vilks, whose images of the prophet Muhammad were among those published in a Danish newspaper in the fall of 2005, prompting violent protests months later. This continues to make him an assassination target for Muslim extremists throughout the world. Communication intercepted by the FBI shows that American Colleen LaRose made killing Vilks "my goal till i achieve it or die trying." She traveled in preparation for an attack and even tried to contact the cartoonist, she admitted in a 2011 guilty plea.

LaRose's plot "seemed to ignite other like-minded people," Vilks told American investigators. His home was targeted by arsonists and he was attacked during a lecture in 2010.

And terrorists from Somalia's al-Shabaab group specifically threatened Vilks in a recruiting video.

"And I say to Lars Vilks, that where you are, if not today or tomorrow, know that we haven't yet forgotten about you." Drawing his finger across his throat, a Swede who joined al-Shabaab named Abu Zaid threatened, "Know what awaits you, as it will be nothing but this, slaughter… and to my brothers and sisters, I call you to make Hijra [emigrate] Inshallah, and if you can, kill this dog Lars Vilks. Then you will receive a great reward from Allah."