Israel has been targeting Iran from the air since last Friday in what it has described as an effort to prevent Tehran from developing nuclear weapons.
According to the International Atomic Energy Agency (IAEA), five nuclear facilities have been struck, sparking fears the air strikes could raise health risks across the region.
Here's what damage has been caused so far and the safety risks of attacking nuclear sites.
What has Israel been targeting?
Several military and nuclear sites in Iran.
Israel says the attacks are to block Iran from developing atomic weapons.
Israeli Prime Minister Benjamin Netanyahu said the operations were to "strike the head of Iran's nuclear weaponization program".
Iran denies ever having pursued a plan to build nuclear weapons and is a signatory to the Nuclear Non-Proliferation Treaty.
It says the nuclear sites it does have are for peaceful purposes.
If Israel continues attacking Iran until it removes the country's nuclear capability, destroying the Fordow enrichment plant is central to its plan.
While another important facility, Natanz, has been hit, the Fordow site would be much harder to target.
This is because it's located inside a mountain, 90-metres underground and can only be reached by American "bunker-buster" bombs, which Israel does not possess.
Why are they being targeted?
Because Israel believes Iran is enriching uranium to levels that could allow it to build a nuclear weapon, despite the Islamic Republic's claims its nuclear work is for "peaceful purposes".
Enriched uranium, specifically uranium-235, is an essential component in many nuclear weapons.
"When you dig uranium out of the ground, 99.3 per cent of it is uranium-238, and 0.7 per cent of it is uranium-235," Kaitlin Cook says, a nuclear physicist at the Australian National University.
"The numbers 238 and 235 relate to its weight — uranium-235 is slightly lighter than uranium-238."
To enrich uranium, basically means increasing the proportion of uranium-235, while removing the uranium-238.
This is typically done with a centrifuge, a kind of "scientific salad spinner" which rotates uranium thousands of times a minute, separating the lighter uranium-235 from the base uranium.
For civilian nuclear power, Dr Cook says uranium-235 is usually enriched to about 3 to 5 per cent.
But once uranium is enriched to 90 per cent, it is deemed weapons-grade.
According to the IAEA, Iran's uranium has reached about 60 per cent enrichment, well on its way to being concentrated enough for a nuclear weapon.
Dr Cook says the process for enriching uranium from 60 per cent to weapons-grade is much easier than it is to get to the initial 60 per cent. That's because there's less uranium-238 to get rid of.
According to the US Institute for Science and International Security, "Iran can convert its current stock of 60 per cent enriched uranium into 233kg of weapon-grade uranium in three weeks at the Fordow plant", which it said would be enough for nine nuclear weapons.
In the hours after Israel attacked Iran last Friday, Netanyahu said Iran was just days away from being able to build nuclear weapons.
In a White House briefing, press secretary Karoline Leavitt said Iran has all it needs to achieve a nuclear weapon.
"It would take a couple of weeks to complete the production of that weapon, which would, of course, pose an existential threat not just to Israel, but to the United States and to the entire world."
But there has been some back and forth between US authorities on whether Iran was really that close to producing nuclear weapons.
In March, US Director of National Intelligence Tulsi Gabbard told members of Congress that Iran was not moving towards building nuclear weapons.
"The IC [intelligence community] continues to assess that Iran is not building a nuclear weapon and Supreme Leader Khamenei has not authorized the nuclear weapons programme he suspended in 2003," she said.
On Air Force One on Monday night, after hastily leaving the G7 summit, President Donald Trump offered a direct contradiction to Ms Gabbard's claims.
"I don't care what she said," Mr Trump said.
"I think they were very close to having it."
What has Israel hit so far?
The IAEA said Israel had directly hit the underground enrichment halls at the Natanz facility, leaving them "severely damaged, if not destroyed all together".
According to the IAEA, the Natanz site was one of the facilities at which Iran was producing uranium enriched up to 60 per cent U-235.
After the attack, the IAEA found radioactive contamination at the site, but it said the levels of radioactivity outside remained unchanged and at normal levels.
Israel Defense Forces spokesperson Effie Defrin said: "We've struck deep, hitting Iran's nuclear, ballistic and command capabilities."
[map]A nuclear complex at Isfahan and centrifuge production facilities in Karaj and Tehran were also damaged.
Israel said on Wednesday it had targeted Arak, also known as Khondab, the location of a partially built heavy-water research reactor.
The IAEA said it had information that the heavy-water reactor had been hit, but that it was not operating and reported no radiological effects.
What are the risks of striking a nuclear site?
Experts say attacks on enrichment facilities are mainly a "chemical problem", not radiological.
Darya Dolzikova, a senior research fellow at London think tank RUSI, says the main concern from destroying an enrichment plant is releasing the harmful uranium hexafluoride gas — highly corrosive and toxic — that's contained in centrifuges.
"When UF6 interacts with water vapour in the air, it produces harmful chemicals," Ms Dolzikova said.
The extent to which any material is dispersed would depend on factors including weather conditions, she added.
"In low winds, much of the material can be expected to settle in the vicinity of the facility; in high winds, the material will travel farther, but is also likely to disperse more widely."
Peter Bryant, a professor at the University of Liverpool who specialises in radiation protection science and nuclear energy policy, says nuclear facilities are designed to prevent the release of radioactive materials into the environment.
"Uranium is only dangerous if it gets physically inhaled or ingested or gets into the body at low enrichments," Professor Bryant said.
While there so far has been no major radiological incidents as a result of the attacks, IAEA director-general Rafael Mariano Grossi stressed the possible nuclear safety and security risks.
"There is a lot of nuclear material in Iran in different places, which means that the potential for a radiological accident with the dispersion in the atmosphere of radioactive materials and particles does exist," he said.
In a post on X, World Health Organization chief Tedros Adhanom Ghebreyesus also voiced his concern about the potential "immediate and long-term impacts on the environment and health of people in Iran and across the region".
What about nuclear reactors?
Well that's a different story.
A strike on Iran's nuclear reactor at Bushehr could cause an "absolute radiological catastrophe", says James Acton, co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace.
While most reactor vessels are protected by steel and concrete containment structures, Dr Cook says the surrounding infrastructure, like spent fuel pools and cooling equipment, would "definitely be a concern" if targeted.
For Gulf states, the impact of any strike on Bushehr would be worsened by the potential contamination of Gulf waters, jeopardising a critical source of desalinated potable water.
In the UAE, desalinated water accounts for more than 80 per cent of drinking water.
While Bahrain and Qatar are fully reliant on desalinated water.
"If a natural disaster, oil spill, or even a targeted attack were to disrupt a desalination plant, hundreds of thousands could lose access to freshwater almost instantly," said Nidal Hilal, professor of engineering and director of New York University Abu Dhabi's Water Research Center.
"Coastal desalination plants are especially vulnerable to regional hazards like oil spills and potential nuclear contamination," he said.
On Thursday, an Israeli military spokesperson said the military has struck the Bushehr nuclear site in Iran.
However, an Israeli military official later said that comment "was a mistake".
The official would only confirm that Israel had hit the Natanz, Isfahan, and Arak nuclear sites in Iran.
Pressed further on Bushehr, the official said he could neither confirm or deny that Israel had struck the location.
Bushehr is Iran's only operating nuclear power plant, which sits on the Gulf coast, and uses Russian fuel that Russia then takes back when it is spent to reduce proliferation risk.
What is heavy water?
Heavy water is H20 made up of hydrogen-2 instead of hydrogen-1.
Dr Cook says it's a little heavier than normal water.
"When you use heavy water, you can run your reactor on non-enriched uranium, avoiding the expense of enriching it in the first place, though the water does cost more.
"But the problem is that heavy-water reactors can also be used to produce plutonium, which can be used in nuclear weapons."
Israel's military said its fighter jets targeted the Arak facility and its reactor core seal to halt it from being used to produce plutonium.
"The strike targeted the component intended for plutonium production, in order to prevent the reactor from being restored and used for nuclear weapons development."
India and Pakistan, both nuclear-armed states, have heavy-water reactors.
So does Israel, but it has never acknowledged having atomic weapons but is widely believed to have them.
ABC with wires
