"Iran's message as always is that terrorism is a global problem, and unity to fight extremism, violence and terrorism with regional and international cooperation is the most important need of today's world," Rouhani said in a statement.
"Undoubtedly, today's terrorist incidents in Tehran will boost Islamic Iran's determination in the fight against regional terrorism, extremism and violence," he said.
Iran "will once again prove that it will break any plots and machinations by ill-wishers with more unity and integrity and its powerful security structure."