The Israeli military said it launched a fresh wave of strikes targeting Iranian ballistic missile and air defence sites on Sunday, while an AFP journalist in Tehran reported hearing loud explosions.
Tehran's enemies Israel and the United States began waves of strikes on Saturday, calling for regime change in Iran and prompting retaliation from the Islamic Republic.
A military statement said Israeli forces had begun "an additional strike wave targeting the ballistic missile array and the aerial defence systems belonging to the Iranian terror regime", without specifying any location.
At least three explosions were heard in Tehran around 0030 GMT, the AFP journalist said.
Israel's military chief Eyal Zamir said on Saturday that the campaign against Iran comes after it "accelerated" its ballistic missile production and continued to promote nuclear weapon research.
"We now face a significant, decisive and unprecedented operation to dismantle the capabilities of the Iranian terrorist regime," he said in a televised statement.