Israel and Iran have targeted each other with missiles. Here’s what you need to know.

Iran and Israel are targeting each other with missiles and air strikes after Israel launched its biggest-ever air offensive against its longtime foe in a bid to prevent it developing a nuclear weapon.

Air raid sirens sounded in Tel Aviv and Jerusalem early on Saturday, sending residents rushing into shelters as successive waves of Iranian missiles streaked across the skies.

The military said its air defence systems were operating.

"In the last hour, dozens of missiles have been launched at the state of Israel from Iran, some of which were intercepted," the Israeli military said.

It said rescue teams were working at a number of locations across the country where fallen projectiles were reported.

In Iran, several explosions were heard in the capital Tehran.

Israeli home front command soldiers next to a building that was hit in an Iranian ballistic missile strike in Ramat Gan. Image: Eyal Warshavsky/SOPA Images/LightRocket via Getty Images .

The Fars news agency said two projectiles hit Tehran's Mehrabad airport, which hosts an air force base.

Israeli media said a suspected missile came down in Tel Aviv, and a Reuters witness heard a loud boom in Jerusalem.

The Fars news agency said Tehran launched waves of air strikes on Saturday after two salvos on Friday night.

One of the waves targeted Tel Aviv before dawn on Saturday, with explosions heard in the capital and Jerusalem, witnesses said.

Those were in response to Israel's attacks on Iran early on Friday against commanders, nuclear scientists, military targets and nuclear sites.

Israel's ambulance service said 34 people were injured on Friday night in the Tel Aviv area, most with minor injuries.

Police later said one person had died.

The US military helped shoot down Iranian missiles headed for Israel on Friday, two US officials said.

Israel's military said Iran fired fewer than 100 missiles on Friday and most were intercepted or fell short.

Several buildings in and around Tel Aviv were hit.

The Israeli strikes on Iran throughout the day and the Iranian retaliation raised fears of a broader regional conflagration, although Iran's allies Hamas in Gaza and Hezbollah in Lebanon have been decimated by Israel.

Iran's state news agency IRNA said Tehran launched hundreds of ballistic missiles at Israel after Israel blasted Iran's huge Natanz underground nuclear site and killed its top military commanders.

Iran denies that its uranium enrichment activities are part of a secret weapons program, saying its nuclear program is for peaceful purposes.

Western countries have long accused Iran of refining uranium at Natanz to levels suitable for a bomb rather than civilian use.

The above-ground pilot enrichment plant at Natanz had been destroyed, UN nuclear watchdog chief Rafael Grossi told the Security Council.

He said the UN was still gathering information about Israeli attacks on the Fordow fuel enrichment plant and a facility at Isfahan.

Iranian Supreme Leader Ayatollah Ali Khamenei accused Israel of starting a war, and a senior Iranian official said revenge would be painful.

Iran's UN envoy Amir Saeid Iravani said 78 people, including senior military officials, were killed in Israel's strikes on Iran and more than 320 people were wounded, most of them civilians.

He accused the US of being complicit in the attacks and said it shared full responsibility for the consequences.

Israeli UN envoy Danny Danon said intelligence had confirmed that within days Iran would have produced enough fissile material for multiple bombs.

He called Israel's operation "an act of national preservation".

The UN nuclear watchdog concluded this week that Iran was in violation of its obligations under the global non-proliferation treaty.

US President Donald Trump said it was not too late for Tehran to halt the Israeli bombing campaign by reaching a deal on its nuclear program.

Tehran had been in talks with the Trump administration on a deal to curb its nuclear program to replace one that Trump abandoned in 2018. Tehran rejected the last US offer.

Talks are due to resume in Oman on Sunday but Iran signalled it might not join.

Feature image: AP Photo/Leo Correa via AAP.