"I was shocked. I had no idea how I was supposed to respond to his mail. I can't describe the feeling, the photos were so horrible," the student, named as Johan, told the Svenska Dagbladet daily.
The teenager was tasked with writing a project about Islam and was told to gather information and attitudes to Islam.
He mailed an address on the Sweden Democrats website intended for "general questions about the Sweden Democrats or the party's national policy" and received a reply from Ted Ekeroth, a Lund county councillor.
Ekeroth sent Johan the link which he explained shows victims of Islamic terrorism in southern Thailand.
The photos include bloodied bodies and body parts including close ups of severely burned corpses and beheaded torsos.
The link was attached in response to a question from the 15-year-old on whether the Sweden Democrats think the media presented a balanced view of Islam.
Ekeroth explained in a mail to SvD that he had warned Johan about the shocking images, adding that he had no idea whether the photos were genuine.
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Sweden Democrat spokesperson Martin Kinnunen has described the material on the website as "unsuitable" and said that it was a mistake for Ekeroth to have sent it.
Kinnunen denied that the incident constitutes a breach of party leader Jimmie Åkesson's call for a zero tolerance policy on racism, but said that Ekeroth would no longer be tasked with answering the party's correspondence.