Why have Israel and Iran attacked each other?

An Israeli missile has hit Iran, US officials have told the BBC's partner CBS News - an attack that is widely seen as its response to Iran's missile and drone attack on Israel.

Iran's own direct attack on Israel - its first ever - was in turn retaliation for an Israeli strike on the Iranian consulate in the Syrian capital Damascus, which killed senior military commanders.

Previously Israel and Iran 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 current 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 previously 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.

The 1 April air strike on an Iranian consulate building in the Syrian capital Damascus killed 13 people. Iran said it was a violation of its sovereignty.

Those killed included Brig Gen Mohammad Reza Zahedi - a senior commander in the Quds force, the overseas branch of Iran's elite Republican Guards (IRGC). He had been a key figure in the Iranian operation to arm the Lebanese Shia armed group Hezbollah.

The consulate attack follows a pattern of air strikes against Iranian targets widely attributed to Israel. Several senior IRGC commanders have been killed in air strikes in Syria in recent months.

The IRGC channels arms and equipment, including high precision missiles, through Syria to Hezbollah. Israel is trying to stop these deliveries, as well as seeking to prevent Iran from strengthening its military presence in Syria.

Iran launched more than 300 drones and missiles towards Israel, the Israeli military said. The attack included 170 drones and 30 cruise missiles and at least 110 ballistic missiles.

Some 99% of the incoming barrage was intercepted either outside Israeli airspace or over the country itself, Israel said. Israel and countries including the US, UK, France and Jordan intercepted drones and cruise missiles while its three-trier umbrella of missile defence systems intercepted ballistic missiles.

Nevertheless, two US officials told CBS news that five ballistic missiles evaded air defences and impacted on Israeli territory. Four landed in the Nevatim air base in the Negev desert in southern Israel - where the country's F-35 fighter jets are based - which the officials said was Iran's primary target. The Israeli military said the base had been "lightly hit".

Tom Fletcher, a foreign policy advisor to several UK prime ministers and a former UK ambassador to Lebanon, said "Iran did telegraph these attacks in advance which made them easier to deter".

Sanam Vakil from the Chatham House think tank said: "The strikes were certainly calibrated, directed to military installations with the aim of not inflicting too much damage or hurting anyone."

US officials have confirmed to the BBC's partner CBS News that an Israeli strike targeted Iran in the early hours of Friday.

It is unclear what type of weapons were used and where they were launched from. US sources said a missile was involved in the attack, while Iran said it had involved small drones.

Iran's Fars news agency said explosions were heard near an army base and air defence systems were activated.

Hossein Dalirian, a spokesman for Iran's National Centre of Cyberspace, said there was "no air attack from outside borders". He said Israel had "only made a failed and humiliating attempt to fly quadcopters [drones] and the quadcopters have also been shot down".

Isfahan province is a large area in the centre of Iran which takes its name from its largest city. The region is home to significant Iranian military infrastructure, including a large airbase, a major missile production complex and several nuclear facilities.

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 its own nuclear weapons but maintains an official policy of deliberate ambiguity.

Iran does not have nuclear weapons and also denies it is attempting to use its civilian nuclear programme to become a nuclear armed state.

Last year the global nuclear watchdog found uranium particles enriched to 83.7% purity - very close to weapons grade - at Iran's underground Fordo site. Iran said "unintended fluctuations" in enrichment levels may have occurred.

Iran has been openly enriching uranium to 60% purity for more than two years in breach of a 2015 nuclear deal with world powers.

However that deal has been close to collapse since US President Donald Trump pulled out unilaterally and reinstated crippling sanctions on Iran in 2018. Israel had opposed the nuclear deal in the first place.

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 its 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.