Israel has carried out attacks on Iran's nuclear facilities, alleging Tehran was getting close to obtaining a nuclear weapon.
Below is a summary of what is known on the subject:
HOW DID ISRAEL EXPLAIN ITS ATTACK?
In a statement on Friday, when the attacks were launched, the Israel Defence Forces said they were revealing for the first time Iran's secret and accelerating plan for the development of a nuclear weapon that could threaten Israel.
Israel has not, however, produced proof that Iran is as close as it now alleges.
The U.N. nuclear watchdog, which carries out inspections in Iran, has said that while it cannot guarantee Iran's nuclear programme is entirely peaceful, it has "no credible indication" of an active, coordinated weapons programme either.
HOW DID WE GET HERE?
As its 2015 nuclear deal with major powers has eroded over the years, Iran expanded and accelerated its nuclear programme, shortening the time it would need to build a nuclear bomb if it chose to - though it denies wanting to.
The 2015 deal introduced strict limits on Iran's atomic activities in exchange for the lifting of sanctions. It slashed Iran's stock of enriched uranium, leaving it only with a small amount enriched to up to 3.67% purity, far from the roughly 90% purity that is weapons grade.
The United States said at the time that a main aim was to increase the time Iran would need to produce enough fissile material for a nuclear bomb - the biggest single hurdle in a weapons programme - to at least a year.
In 2018, during his first term, President Donald Trump pulled the United States out of the deal, reimposing sanctions on Tehran that slashed its oil sales and battered its economy. In 2019, Iran started breaching the restrictions on its nuclear activities and then pushed far beyond them.
It went on to breach all the deal's key restrictions, including on where, with what machines and to what level it can enrich uranium, and how much material it can amass.
Its stock of enriched uranium, which was capped at 202.8 kg under the deal, was estimated at 9.2 tonnes in May, according to the latest quarterly International Atomic Energy Agency report.
HOW FAR HAS IRAN GOT?
The exact status of various Iranian nuclear facilities and material since Israel's strikes is unclear.
At least until Israel's attacks, Iran was enriching uranium to up to 60% purity and had enough material at that level for nine nuclear weapons if enriched further, according to a theoretical IAEA yardstick.
That means Iran's so-called "breakout time" - the time it would need to produce enough weapons-grade uranium for a nuclear bomb - was close to zero, likely a matter of days or little more than a week, analysts say.
Iran had three operating enrichment facilities: an above-ground plant and a larger, underground one at its Natanz complex and another buried inside a mountain at Fordow.
Only Fordow appears to have been spared damage, the IAEA has said. The above-ground plant has been destroyed and the underground one at Natanz has likely had its uranium-enriching centrifuges badly damaged or destroyed, IAEA chief Rafael Grossi has said.
That will have lengthened its breakout time at least somewhat because far fewer centrifuges if any are operating. The status of its stock of enriched uranium is also unclear.
HOW FAST COULD IRAN SPRINT TO A BOMB?
Aside from uranium enrichment, there is the question of how long it would take Iran to produce the rest of a nuclear weapon and possibly make it small enough to put in a delivery system like a ballistic missile, should it choose to. This is much harder to estimate as it is less clear how much knowledge Iran has.
Estimates of how long Iran would need for weaponisation generally vary between months and about a year.
"Certainly it was not for tomorrow... I don't think it was a matter of years," Grossi told CNN on Tuesday when asked how long it would have taken Iran to produce a bomb.
AND WOULD IT?
U.S. intelligence agencies and the IAEA believe Iran had a coordinated nuclear weapons programme that it halted in 2003. It worked on aspects of weaponisation and some work continued until as late as 2009, the IAEA found in a 2015 report. Grossi said this month its latest findings still broadly fit with that.
Iran denies ever having a nuclear weapons programme, though Supreme Leader Ali Khamenei has said that if it wanted to world leaders "wouldn't be able to stop us".
The IAEA has said it has concerns about statements by former senior officials about Iran's ability to make a bomb.
Diplomats said those statements included a television interview by Iran's former nuclear chief Ali Akbar Salehi in which he likened producing a nuclear weapon to building a car, saying Iran knew how to make all the parts needed.
As a result of Iran ceasing to implement elements of the 2015 deal, the IAEA can no longer fully monitor Iran's production and inventory of centrifuges and it can no longer conduct snap inspections. That has prompted speculation about whether Iran could have set up a secret enrichment site, but there are no concrete indications of one.
