Fars said the blast occurred shortly after mid-day and was felt across the city. It was not clear whether there were any casualties.
"The blast was very strong. It shook the city. But the reason behind the blast is still unknown," Fars said, without quoting a source.
Tabriz is the capital of Iran's Northeastern Azerbaijan province.
"The windows of many buildings were shattered from the blast," the agency said.
Iran often blames blasts in outlying provinces on foreign agents.
The majority of the population in Tabriz are Azeris and speak a language closely related to Turkish. They make up about 25 percent of the population in the Islamic Republic of Iran.
Güncelleme Tarihi: 25 Şubat 2008, 11:50