STOCKHOLM (AP) — Dozens of angry youths in southwestern Sweden pelted police with rocks and bottles in unrest apparently triggered by derogatory material published on the Internet.

No injuries were reported Tuesday, but police detained 27 youths in the clashes at the Plus High School in Goteborg, Sweden's second-largest city.

Swedish public television said the students were upset over photos and sexually explicit texts about local teenagers that someone posted on photo-sharing site Instagram.

Police said in a statement they were investigating whether the publication amounted to defamation. They were also reviewing footage of the clashes to determine if anyone involved could be charged with rioting.

Separately, Instagram faced a storm of outrage after a change in its user agreement hinted that it might use shared photos in ads.