The International Atomic Energy Agency (IAEA) has started investigation on the possible military dimension of Iran's nuclear program, an agency official said Monday.

Speaking to reporters at the Vienna airport, IAEA Deputy Director General Tero Varjoranta said the nuclear watchdog has just taken the first step to investigate the long-existing suspicion.

Iran and the IAEA have recently agreed on seven practical measures to be implemented by Tehran by May 15 to promote the investigation of Iran's nuclear program.