Iran who had been on high alert after Israel said it would respond to an Iranian attack against it on Saturday night.
Iran who had launched its unprecedented attack in retaliation for an Israeli air strike on a consulate building in Syria on 1 April, which killed two top generals, and had signalled that it did not seek further escalation.
The International Atomic Energy Agency (IAEA), has said no nuclear sites were damaged. There has been no official Israeli comment.
The explosions was said to be heard near Isfahan International Airport and an army base in Isfahan city, activating local air defence systems. Isfahan province is home to a large airbase, a major missile production complex and several nuclear facilities.
In recent days, Iranian leaders had warned that any Israeli attack on Iran would trigger a swift response. There have been attempts among the international community to de-escalate the crisis, with calls for restraint.
UN Secretary General António Guterres said there had been “perilous escalation” between Israel and Iran.
“One miscalculation, one miscommunication, one mistake, could lead to the unthinkable – a full-scale regional conflict that would be devastating for all involved,” he told the Security Council.