Israel's air force attacked targets in western and central Iran early on Monday, the Israeli military said on Telegram, without initially providing further details.
Iranian state broadcaster IRIB and the IRNA news agency reported that explosions had been heard in the capital Tehran. Residential areas were not hit, according to the reports.
The attack followed Iranian missile strikes on Israel the previous evening.
Late on Sunday, state media in the Islamic Republic reported several waves of missiles had been fired at its arch-enemy. According to the Israeli military, all missiles in the first waves were intercepted.
Earlier on Sunday, Israel had attacked suburbs of the Lebanese capital Beirut despite a ceasefire announced by US President Donald Trump.
Israeli Prime Minister Benjamin Netanyahu and Defence Minister Israel Katz said the military had targeted "terrorist" headquarters after the Iran-backed Hezbollah militia fired at Israel.
Hezbollah is Iran's most important non-state ally. Tehran had previously warned that further Israeli attacks on the greater Beirut area would be viewed as a new escalation.
Israel significantly scaled back its attacks in the Beirut area after an official ceasefire came into effect in mid-April. Trump had also announced a halt to Israeli attacks there and an end to Hezbollah attacks on Israel.
However, Israel had threatened to strike those areas again in the event of Hezbollah attacks on Israel, urging residents of the suburbs to flee.
