Billions of dollars of Iranian money continues to be frozen in South Korean banks as its prime minister visits Tehran.
Iran’s nuclear programme has been targeted in sabotage attacks over the last decade, the latest incident striking its underground Natanz facility.
The attack at Natanz on Sunday comes as world powers try to negotiate a return by Iran and the United States to Tehran’s atomic accord and threatens to upend those negotiations and further heighten regional tensions across the Middle East.
Iran’s nuclear programme began with the help of the US. Under its “Atoms for Peace” initiative, Washington supplied a test reactor that came online in Tehran in 1967 under the rule of Shah Mohammad Reza Pahlavi. That help ended once Iran’s 1979 Islamic Revolution overthrew the shah.
In the 1990s, Iran expanded its programme, including secretly buying equipment from Pakistan’s top nuclear scientist, Abdul Qadeer Khan.
Khan’s designs allowed Iran to build the IR-1 centrifuges that largely power its uranium enrichment.
Tehran insists its nuclear programme is peaceful but the International Atomic Energy Agency (IAEA) says Iran “carried out activities relevant to the development of a nuclear explosive device” in a “structured” programme through the end of 2003.
Natanz, in Iran’s central Isfahan province, hosts the country’s main uranium enrichment facility.
Iran has one operating nuclear power plant in Bushehr, which it opened with Russia’s help in 2011.
Iran previously reconfigured its Arak heavy-water reactor so it could not produce plutonium.
Its Fordo enrichment site is also dug deep into a mountainside. Tehran also still operates the Tehran research reactor.
Iran struck the nuclear deal in 2015 with China, France, Germany, Russia, the United Kingdom and the United States.
The deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), saw Iran dramatically limit its enrichment of uranium under the watch of IAEA inspectors in exchange for the lifting of economic sanctions.
The small stockpile of less-enriched uranium blocked Iran from having enough material to build a nuclear bomb if it chose.
Then-President Donald Trump unilaterally withdrew the US from the accord in 2018.
Since the US withdrawal, Iran has in response abandoned all the deal’s limits on its uranium enrichment.
It spins advanced centrifuges, grows its stockpile and enriches up to 20-percent purity – a technical step away from weapons-grade levels of 90 percent.
President Joe Biden, who took office in January, has said he is willing to re-enter the nuclear deal.
Countries began negotiations in Vienna last week seeking to find a way forward.
Israel, which under Netanyahu has vowed not to see the deal revived, is suspected of recently stepping up a shadow campaign targeting Iran.
The head of Iran’s civilian nuclear programme described the sabotage of Natanz on Sunday as “nuclear terrorism”. But it only marked the latest attack targeting the Iranian programme.
Natanz found itself first targeted by a major cyberattack in the late 2000s.
Called Stuxnet, the virus attacked control units for its centrifuges, causing the sensitive devices to spin out of control and destroy themselves.
Experts widely attribute the attack to the US and Israel, as does Iran.
Another sabotage attack targeted Natanz in July last year. An explosion ripped apart an advanced centrifuge assembly plant at the site.
Afterwards, Iran said it would rebuild the site deep inside a nearby mountain. Satellite photos show that work continues. Suspicion widely fell on Israel for the blast as well.
Then there have been a series of assassinations targeting Iranian nuclear scientists over the last decade. The killings involved bombings and shootings.
The most recent killing saw the assassination of high-ranking Iranian nuclear physicist Mohsen Fakhrizadeh – named by the West as leading Iran’s military nuclear programme until it was disbanded in the early 2000s – in November. Iran blames Israel for those slayings.