An Israeli missile has hit Iran, US officials have told the BBC’s partner station CBS News.
Blasts were heard in the central province of Isfahan and flights have been suspended over several cities, Iranian media say.
Iran is on high alert after Israel said it would respond to an Iranian attack against it on Saturday night.
Iran fired more than 300 drones and missiles in its first ever direct attack on Israel.
Almost all were intercepted by Israeli air defences with support from the US, UK and other allies.
Iranian media has not reported any direct impacts and has said all the nuclear facilities are safe. The Israeli military has not commented.
Isfahan province is home to a large air base, a major missile production complex and several nuclear sites.
Iran’s Fars news agency says explosions have been heard near Isfahan international airport and an army base in Isfahan city, activating local air defence systems.
Video from Isfahan posted on BBC Persian’s Instagram account shows orange flashes in the night sky and the sound of what appears to be bursts of anti-aircraft fire.
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.
On Thursday, 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.