Iran's intelligence services said Monday they have arrested suspects in the assassination a year ago of a nuclear physicist in a months-long covert operation that also led them to penetrate Israel's Mossad spy agency.
Iran blames the Mossad for the slaying of Tehran University physics professor Masoud Ali Mohammadi, who was killed by a bomb-rigged motorcycle that exploded outside his house as he was leaving for work in January 2010. Possible explanations for why he was targeted have never been clear, particularly as he had no known link to Iran's nuclear work, but Iranian state media have presented it as an attempt to slow the atomic program.
Monday's announcement said Iranian agents arrested a network of spies linked to the slaying, opening up revelations about further Israeli plots against the country, including a campaign to assassinate nuclear scientists.
"After months of silent struggle, offensive, multilayered and complicated operations and penetration into the depths of the Zionist regime's intelligence led to the uncovering of very important and sensitive information about Mossad spies and operations," said the Intelligence Ministry statement read out on state TV.
"Heavy blows were inflicted on the structure of the Zionist intelligence and security services."
The United States, Israel and other nations believe Iran is intent on developing nuclear weapons under the cover of a civil atomic energy program. Iran insists its work is solely for peaceful purposes.
Later Monday, Iran's state TV broadcast confessions of one of those arrested in which the unidentified young man said he underwent training in Israel on how to place bombs on cars.
The man, whose face was visible, said he received training at a military camp located between Tel Aviv and Jerusalem.
"Two new Iranian-made motorbikes were there ... they told me where to go, where to stop, who to call and how to do things back in Iran," he said.
In Israel, officials in Prime Minister Benjamin Netanyahu's office had no immediate comment on Monday's announcement.
A pair of bomb attacks in November killed one nuclear scientist and wounded another in the capital. While those attacks targeted two people who had high-level involvement in Iran's nuclear work, a motive behind the slaying of Mohammadi is less clear.
The 50-year-old professor had no prominent political voice, no published work with military relevance and no declared links to the country's nuclear program, though his work included some aspects of nuclear theory.
Nonetheless, the Intelligence Ministry said in Monday's statement that the investigation into his death led authorities back to the Mossad and to the conclusion that Israeli spies operating from Europe and from countries neighboring Iran were directing a campaign to kill Iranian nuclear scientists. It offered no details.
"After extensive security measures and precise intelligence tracking ... the main agents behind this terrorist crime were identified and arrested, and a network comprising spies and terrorists affiliated to the Zionist regime was destroyed," it said.
Besides November's bomb attacks, the country's nuclear work faced a number of challenges over the past year, from malfunctioning centrifuges that spun out of control to a highly complex computer worm — known as Stuxnet — that Iran said was aimed at sabotaging its uranium enrichment program.
Iran is also under four sets of U.N. and other international sanctions over its refusal to stop enriching uranium, the cornerstone of the program.
A week ago, Israel's newly retired spy chief, Meir Dagan, said Iran would not be able to build a nuclear bomb before 2015 — further pushing back Israeli intelligence estimates of when Tehran might become a nuclear power.
The former Mossad chief said Thursday that Iran's nuclear program had been delayed by unspecified "measures" employed against it, according to the Israeli daily Yediot Ahronot.
In November's attacks, which took place on the same day, assailants on motorcycles attached magnetized bombs to the two men's cars as they drove to work.
They detonated seconds later, killing one of them, Majid Shahriar, and wounding the other, Fereidoun Abbasi. Each of their wives, who were in the cars, were also wounded.
Abbasi is on a list of figures suspected of links to secret nuclear activities in a 2007 U.N. sanctions resolution, which puts a travel ban and asset freeze on those listed. The resolution describes him as a Defense Ministry scientist who works closely with Mohsen Fakhrizadeh, believed to head secret nuclear projects. Iranian media said he was a member of the Revolutionary Guard, Iran's strongest military force.
Abbasi, according to pro-government news websites, is also a laser expert and one of the few top Iranian specialists in nuclear isotope separation.
Shahriar was involved in a major project with Iran's nuclear agency, the agency's chief said at the time of the killing, though he did not give specifics.
Iran's intelligence agency has already announced a number of arrests in the November bombings.
In 2007, nuclear scientist Ardeshir Hosseinpour died from gas poisoning. A one-week delay by state media in reporting his death prompted speculation about the cause, including that the Mossad was to blame.