Why has Israel attacked Iran?

Israel has carried out a series of overnight air strikes on Iran, hitting what Israel called "military targets".

An attack had been expected for weeks in retaliation for an Iranian missile attack on Israel.

Israel had vowed to hit back after Iran carried out a ballistic missile attack on Israel on 1 October. In that attack, Iran fired more than 180 missiles at Israel. Most were intercepted by Israel's air defences and US-led allied forces. Some though hit air bases and other sites. One Palestinian was killed by a falling missile casing.

Israel said it would retaliate, but did not say when or how. There had been constant speculation since then on the timing of an Israeli attack and what form it might take - from limited strikes to massive attacks on Iran's oil fields and nuclear sites.

The attack came in the early hours of Saturday and appears to have been restricted to missile manufacturing and launching sites, and what Israel called "other aerial capabilities", without being specific.

Iran said it attacked Israel on 1 October in retaliation for the killings of the leaders of Hezbollah and Hamas - Iranian-backed armed groups fighting Israel - and a senior Iranian commander.

Hezbollah leader Hassan Nasrallah and Brig Gen Abbas Nilforoushan were killed when Israel bombed the building they were in in the Lebanese capital, Beirut, on 27 September. Hamas political chief Ismail Haniyeh was killed in an explosion in the compound where he was staying on a visit to Tehran on 31 July. Iran blamed Israel for that attack, though Israel has neither confirmed nor denied involvement.

Iran's attack was its second-ever directly against Israel. It came five months after it first attacked Israel with waves of about 300 drones and missiles. Israel said almost all were intercepted. That attack was in response to an Israeli air strike on an Iranian consulate complex in the Syrian capital, Damascus, on 1 April, which killed 13 people, including seven members of Iran's overseas Quds Force. Two of those killed were a senior Quds Force commander and his deputy. Iran said the attack was a violation of its sovereignty.

The Quds Force is part of Iran's most powerful armed force, the Islamic Revolutionary Guard Corps (IRGC).

The IRGC channels arms and equipment, including high precision missiles, through Syria to Hezbollah.

Israel retaliated for Iran's missile and drone attack nearly three weeks later by attacking targets in Iran's central Isfahan region. US officials confirmed the Israeli attack, though Israel did not comment. Israeli drones are reported to have hit radar for Iran's Russian-made S-300 air defence missile system, which Israel believes would pose a particularly dangerous threat to any of its fighters planes in nearby air space.

The attack on the radar was considered limited and designed to signal Israel's ability to strike Iranian military assets.

Prior to Iran's direct attack on Israel on 1 April, Iran and Israel had been engaged in a years-long shadow war - attacking each other's assets without admitting responsibility.

Those attacks have ratcheted up considerably during the war in Gaza sparked by the Palestinian group Hamas's assault on nearby Israeli communities last October.

The two countries were allies until the 1979 Islamic revolution in Iran, which brought in a regime that has used opposing Israel as a key part of its ideology.

Iran does not recognise Israel's right to exist and seeks its eradication. The country's supreme leader, Ayatollah Ali Khamenei, has called Israel a "cancerous tumour" that "will undoubtedly be uprooted and destroyed".

Israel believes that Iran poses an existential threat as evidenced by Tehran's rhetoric, its build-up of proxy forces in the region including the Lebanese Shia militant group Hezbollah that are sworn to Israel's destruction, and its funding and arming of Palestinian groups including Hamas.

It also accuses Iran of secretly trying to develop nuclear weapons, though Iran denies seeking to build a nuclear bomb.

Iran is much bigger than Israel geographically and has a population of nearly 90 million, nearly ten times as big as Israel's - but this does not translate into greater military power.

Iran has invested heavily in missiles and drones. It has a vast arsenal of its own, but has also been supplying significant amounts to its proxies - the Houthis in Yemen and Hezbollah in Lebanon.

What it lacks is modern air defence systems and fighter jets. Russia is believed to be co-operating with Iran to improve those, including by providing Su-35 fighter jets, in return for the military support Tehran has given Moscow in its war on Ukraine.

By contrast, Israel has one of the most advanced air forces in the world. According to the IISS military balance report, Israel has at least 14 squadrons of jets - including F-15s, F-16s and the latest F-35 stealth jet.

Israel also has experience of conducting strikes deep inside hostile territory. The shortest distance between Iran and Israel is about 1,000km (620 miles).

Israel is assumed to have nuclear weapons but maintains an official policy of ambiguity. Iran does not have nuclear weapons though Western states suspect it of secretly aiming to develop them. Iran emphatically denies it is trying or even wants to obtain nuclear weapons.

Like Israel, Iran has a civilian nuclear programme, though it has been under suspicion for decades of covertly running a parallel programme to manufacture material - enriched uranium - for nuclear bombs, and the missiles to deliver them.

In May, the head of the global nuclear watchdog said Iran was "weeks rather than months" away from having enough material for a nuclear bomb. However, this does not mean Iran is weeks away from a bomb. It would still require a final step of enriching that material to military grade, and having warheads, which it is not believed to possess.

Israel is not a signatory to the nuclear Non-Proliferation Treaty (NPT), though Iran is. The NPT aims to stop the spread of nuclear weapons and requires members to open their nuclear facilities to inspection to verify they are being used for purely peaceful purposes.

A 2015 UN-backed deal with Iran under which it agreed to measures limiting its nuclear activities in return for a lifting of economic sanctions largely collapsed after then-President Trump pulled the US out in 2018. Iran has stepped up its nuclear programme since then.

Iran has built up a network of allies and proxy forces in the Middle East that it says form part of an "axis of resistance" challenging US and Israeli interests in the region. It supports them to varying degrees.

Syria is Iran's most important ally. Iran, along with Russia, helped the Syrian government of Bashar al-Assad survive the country's decade-long civil war.

Iran's relationship with Russia is also becoming increasingly significant. In December the Russian foreign ministry said the countries would speed up work on a "major new interstate agreement".

Iran has provided Russia with Shahed attack drones. In February, Reuters quoted sources as saying Iran had also provided ballistic missiles. Iran denied the report. Meanwhile Iran says Russia plans to provide Iran with more advanced aircraft.

Of the armed groups that Iran backs, Hezbollah in Lebanon is the most powerful. It has been trading cross-border fire with Israel on an almost daily basis since war erupted between Israel and Hamas. Tens of thousands of civilians on both sides of the border have been forced to leave their homes.

Iran backs several Shia militia in Iraq which have attacked US bases in Iraq, Syria and Jordan with rocket fire. The US retaliated after three of its soldiers were killed at a military outpost in Jordan.

In Yemen, Iran provides support to the Houthi movement, which controls the most populated areas of the country. The Houthis have fired missiles and drones at Israel and have also been attacking commercial shipping near Yemen's shores, sinking at least one vessel. The US and UK have struck Houthi targets in response.

Iran also provides weapons and training to Palestinian armed groups including Hamas, which attacked Israel on 7 October last year. However, Iran denies any role in the 7 October attack itself.