"In the past few days, a number of opportunists, who were guided from outside Iran, distributed pamphlets to call for a gathering in Tabriz for the first anniversary," said Tabriz chief prosecutor Yusef Firouzi.
"In recent days, 15 have been arrested and we are currently interrogating them," he said.
The Iran newspaper in May 2006 published a cartoon depicting an ethnic Azeri as a cockroach, sparking days of clashes between police and thousands of people which left four dead.
Azeris form a majority in East Azarbaijan, West Azarbaijan and Ardebil provinces. They are Shiites who speak a Turkic language and are well integrated into Iranian society.