Fars said the blast occurred shortly after midday 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.
- http://www.swissinfo.ch/eng/news/international/Blast_shakes_northwestern_city_in_Iran.html?siteSect=143&sid=8778732&cKey=1203933302000&ty=ti