Iran's senior military officials said the war would "spread in the coming days to all areas occupied by this [Israeli] regime and American bases".

The U.S. says it wasn't involved in the strikes on Iran, but three American officials told NBC News the U.S. is assisting in shooting down Iranian missiles and projectiles targeting Israel.

The Lebanese militant group Hezbollah was long considered Iran’s first line of defense in case of a war with Israel.

Israel and Iran have opened a new chapter in their long history of conflict. Israel launched a major attack with strikes early Friday that set off explosions in the Iranian capital of Tehran.

For years, Israel and Iran engaged in a shadow war, a series of mostly quiet, often deniable attacks, with Iran frequently operating through allied proxy groups.

Israel launched a sweeping air assault on Iran on Friday, hitting 100 targets – including nuclear and military facilities in Tehran and killing

The Israeli military on Sunday released video it said showed the underground rooms where they found the body of Hamas leader Mohammed Sinwar who is believed to have died in tunnels under a Gaza hospital last month.

The IDF has confirmed that senior Hamas leader Mohammed Sinwar was killed in a May 13 airstrike targeting an underground command center beneath a hospital in Khan Younis, Gaza. Sinwar had succeeded his brother Yahya Sinwar as head of Hamas after Yahya and Mohammed Deif were killed last year.

Iran and Israel targeted each other with airstrikes early on Saturday after Israel launched its biggest-ever offensive against its longtime foe in a bid to prevent it from developing a nuclear weapon.