Why did US and Israel attack Iran and how long could the war last?

Conflict has spread across the Middle East after Iran's Supreme Leader Ayatollah Ali Khamenei was killed during strikes launched by the US and Israel on Saturday, which were followed by a call from US President Donald Trump for Iranians to overthrow the government.

Iran has responded by launching missiles and drones across the region, targeting Israel, Bahrain, Kuwait, Qatar, the United Arab Emirates, Jordan, Saudi Arabia, Cyprus and ships passing through the Strait of Hormuz.

On Monday, the Iran-backed Shia militia group Hezbollah joined the fighting, launching rockets into Israel from its bases in Lebanon.

Here is how the US and Israel's war with Iran has unfolded so far, how it has impacted the region and how long it could last.

What has been happening in Iran?

The US and Israel launched widespread strikes on Saturday targeting Iran's missile infrastructure, military sites and senior leaders.

The Israel Defense Forces (IDF) said dozens of senior Iranian political figures and leaders within the powerful Islamic Revolution Guard Corps (IRGC) were also killed, including Defence Council secretary Ali Shamkhani, Defence Minister Brig Gen Aziz Nasirzadeh and IRGC commander Gen Mohammad Pakpour.

The IRGC has since named a new commander in chief, Ahmad Vahidi.

As of Monday, the Iranian Red Crescent said 555 people in 130 locations had been killed. According to Iranian officials, more than 150 people, including children, were killed in a strike on a school in southern Iran close to an IRGC base.

Internet connectivity in Iran has been almost entirely restricted and its airspace is closed, though Iran's military continued to have the capacity to launch retaliatory attacks.

The US and Israel carried out more strikes on Sunday, hitting the capital and elsewhere. Trump said nine Iranian naval ships had been sunk and Iran's naval headquarters destroyed.

Why have the US and Israel attacked Iran?

Trump has said the aim of the operation is to "ensure that Iran does not obtain a nuclear weapon".

"We're going to destroy their missiles and raze their missile industry to the ground. It will be totally again obliterated," he said in an eight-minute video posted on Truth Social on Saturday morning.

He also warned Iran's armed forces to lay down their weapons in return for "complete immunity", or "face certain death".

Trump urged Iranian people to prepare to overthrow the clerical establishment: "When we are finished, take over your government. It will be yours to take. This will be probably your only chance for generations."

The massive military operation - which the US has dubbed Operation Epic Fury - comes after weeks of threats from Trump that he would order military action if Iran did not agree to a new deal over its nuclear programme.

Iran has repeatedly said its nuclear activities are entirely peaceful.

The US military Central Command said they wanted to "dismantle the Iranian regime's security apparatus, prioritising locations that posed an imminent threat".

Earlier, Israeli Prime Minister Benjamin Netanyahu said Israel and the US had launched the "operation to remove the existential threat posed by the terrorist regime in Iran".

Iran has described the attacks as "unprovoked, illegal and illegitimate", and has carried out widespread attacks across the region in response.

Iran has launched ballistic missiles and drones at Israel, several Middle Eastern countries with links to the US, a British military base in Cyprus and ships off the Iranian coast.

The IRGC said it had targeted Israeli government and military sites in Tel Aviv and elsewhere, while nine people were killed when a residential area in Beit Shemesh was hit.

The UK Ministry of Defence (MoD) has confirmed a drone struck the British Akrotiri base in Cyprus. No one was killed or injured in the attack but the MoD said some people were being moved off the RAF base.

Qatar, Bahrain, Jordan, the United Arab Emirates and Kuwait - all home to US military bases - have been targeted, as have Oman and Saudi Arabia.

More strikes were heard across the Gulf on Monday, including in the cities of Dubai, Doha and Manama. Iran's military said it used 15 cruise missiles in attacks on a US airbase in Kuwait and vessels in the Indian ocean.

Civilian sites, including hotels in Dubai, have been struck as well as military installations.

The US and Arab allies issued a joint statement condemning Iran's attacks on the Gulf states, saying "the targeting of civilians and of countries not engaged in hostilities is reckless and destabilising behaviour".

On Monday, three American jets were shot down over Kuwait in what the US military said appeared to be a friendly fire incident. The pilots survived.

Over the weekend, the US military confirmed three soldiers were killed and five more injured. CBS News, the BBC's US news partner, said they were killed during operations launched from Kuwait.

The US military confirmed a fourth death on Monday without providing further details.

A new front in the conflict opened on Monday morning when Hezbollah attacked Israel, prompting the IDF to strike targets in the capital Beirut and in southern Lebanon.

The armed group is allied to Iran's government and said it was seeking to avenge Khamenei's assassination.

Lebanese officials say dozens have been killed or injured in the strikes so far, while Israel urged people living in 50 villages to evacuate in anticipation of further operations which could last "several days".

How is the war impacting the economy and energy prices?

Instability in the Middle East has begun to impact global economy, particularly due to the Gulf's critical energy industry being targeted.

Iranian drones have attacked the Ras Tanura refinery in Saudi Arabia, causing a partial shutdown, the country's energy ministry said on Monday.

Qatar's state-run energy firm said it had halted liquefied natural gas production due to Iranian attacks, causing a spike in gas prices.

Iran warned vessels not to pass through the Strait of Hormuz, a major shipping channel through which about 20% of the world's oil and gas is shipped.

There has been a 10% surge in the global price of oil - sparking fears of petrol prices rising and wider knock-on effects for the international economy. Natural gas prices have also surged by as much as 25%.

How might Khamenei's successor be chosen?

Iran has said it will appoint a new supreme leader swiftly. A transitional leadership council has been formed to run the country temporarily, consisting of: President Masoud Pezeshkian, judiciary chief Gholamhossein Mohseni Ejei and senior cleric Alireza Arafi.

The formal selection of a new supreme leader is decided by 88 senior clerics known as the Assembly of Experts.

Under the country's constitution, these clerics must select the new supreme leader as soon as possible, but this may prove difficult for safety reasons while the country is under attack.

Is it safe to travel to the region and how long could the war last?

On Saturday, Trump said the attacks on Iran would "continue, uninterrupted throughout the week or, as long as necessary", but has since suggested a longer time frame.

The US president told the New York Times on Sunday that the US and Israel could maintain operations at the same tempo for four to five weeks, and told the Daily Mail it could last "four weeks or less".

On Saturday, Netanyahu said "this campaign will continue as long as it is needed".

Thousands of flights have been grounded to and from the region, in one of the most serious disruptions to global travel since the Covid-19 pandemic.

Wizz Air has suspended flights until 7 March in Israel, Dubai and Abu Dhabi in the UAE, Amman in Jordan, and in Saudi Arabia until Tuesday.

British Airways has cancelled flights to Tel Aviv and Bahrain until Wednesday.

Qatar Airways confirmed flight operations "remain temporarily suspended due to the closure of Qatari airspace".

Kuwait's aviation authority said it was halting all flights to Iran until further notice, according to state media.

Emirates has temporarily suspended its operations to and from Dubai. Lufthansa, Air India, Virgin Atlantic and Turkish Airlines have also announced cancellations.

Some countries in the region - including Iraq and Jordan - have also closed their airspace. The UAE said it has "partially and temporarily" closed its airspace as a precaution, state media reported.

With additional reporting by Robert Greenall, Hafsa Khalil and BBC Persian.