An Iranian nuclear scientist was killed on Wednesday in the latest in a series of mysterious attacks on scientists in the country since 2009.
Iran says its nuclear program is purely for civilian use but Western powers believe it has military goals.
Here are some details on scientists in Iran and events linked to them over the last three years:
- Shahram Amiri said he was kidnapped in June 2009 when on a pilgrimage in Saudi Arabia and transferred to the United States. He said he was offered $50 million to remain in America and "to spread lies" about Iran's nuclear work.
- Before his disappearance, Amiri worked at Iran's Malek Ashtar University, an institution closely connected to the country's Revolutionary Guards. Tehran initially refused to acknowledge Amiri's involvement in Iran's nuclear program.
- Amiri returned to Tehran in July 2010. Washington denied kidnapping him and insisted he had lived freely in the United States.
- Nuclear scientist Massoud Ali-Mohammadi was killed by a remote-controlled bomb in Tehran on January 12. Some opposition websites said he had backed moderate candidate Mirhossein Mousavi in the disputed 2009 election that secured President Mahmoud Ahmadinejad's return to power.
- Iranian officials described the physics professor as a nuclear scientist but a spokesman said he did not work for the Atomic Energy Organisation. He lectured at Tehran University.
- Western sources said the professor worked closely with Mohsen Fakhrizadeh-Mahabadi and Fereydoun Abbassi-Davani, both subject to U.N. sanctions because of their work on suspected nuclear weapons development.
- A list of Ali-Mohammadi's publications on Tehran University's website suggested his specialism was theoretical particle physics, not nuclear energy, a Western physics professor said.
* Two car bomb blasts killed an Iranian nuclear scientist and wounded another in Tehran on November 29 in what Iranian officials called an Israeli or U.S.-sponsored attack on its atomic program.
- Majid Shahriyari was killed and his wife was injured. Iran's atomic energy agency chief Ali Akbar Salehi said Shahriyari had a role in one of its biggest nuclear projects, but did not elaborate, the official news agency IRNA reported. He was a lecturer at Shahid Beheshti University.
- In the other blast Fereydoun Abbasi-Davani and his wife were both wounded. Abbasi-Davani, head of physics at Imam Hossein University, has been personally subject to U.N. sanctions because of what Western officials said was his involvement in suspected nuclear weapons research.
- Intelligence Minister Heydar Moslehi later said: "This terrorist act was carried out by intelligence services such as the CIA, Mossad and the MI6. A group that wanted to carry out a terrorist act but did not succeed, was also arrested. They confessed that they were trained by these intelligence services."
- In February 2011 President Mahmoud Ahmadinejad appointed Fereydoun Abbasi-Davani as vice-president and head of the Atomic Energy Organisation, Fars news agency reported.
* Physicist Darioush Rezai, 35, was shot dead by gunmen in eastern Tehran on July 23. The university lecturer had a PhD in physics. Deputy Interior Minister Safarali Baratlou said he was not linked to Iran's nuclear program after early reports in some media said he was.
* Mostafa Ahmadi-Roshan, a 32-year-old graduate of chemical engineering was killed by a bomb placed on his car by a motorcyclist in Tehran. Another passenger died in hospital and a pedestrian was also injured. The attack was similar to that in November 2010.
- Iran said the victim was a nuclear scientist who supervised a department at Natanz Uranium Enrichment Facility. Iran blamed Israel and the United States for the attack. (Reporting by David Cutler, London Editorial Reference Unit; editing by David Stamp)