(Reuters) - Iran has hanged a man it said was an agent for Israeli intelligence agency Mossad whom it convicted of killing one of its nuclear scientists in 2010, Iranian state media reported on Tuesday.

Tehran has accused Israel and the United States of assassinating four Iranian scientists since 2010 in order to sabotage its nuclear program which the West suspects is hiding Iran´s attempt to develop a nuclear weapons capability.

While Israel has declined to comment on the killings, it regards Iran´s nuclear program as an existential threat and has threatened military action against Tehran. Washington has denied any U.S. role.

Twenty-four year old Majid Jamali Fashi was hanged at Tehran´s Evin Prison after being sentenced to death in August last year for the murder of Massoud Ali-Mohammadi, Iran´s state news agency quoted the central prosecutor´s office as saying. It said he had confessed to the crime.

Ali-Mohammadi was killed in January 2010 when a remote-controlled bomb attached to a motorcycle outside his home in Tehran went off.

Tuesday´s report said Fashi had confessed to travelling to Tel Aviv to receive training from Mossad before returning to Iran to plot the assassination.

A spokesman for Iran´s Atomic Energy Organization said at the time that Ali-Mohammadi, a 50-year-old Tehran University professor, was not involved in its activities.

The most recent attack on an Iranian scientist occurred in January. Mostafa Ahmadi-Roshan - a deputy director of the Natanz uranium enrichment facility - was killed when a magnetic bomb planted on his vehicle detonated.

Israel has a policy of not commenting on the allegations but an unnamed Israeli source previously said the daylight killings provoked panic in surviving colleagues and generate a phenomenon Mossad veterans dub "virtual defection" which hinders Iran´s nuclear progress.

Last month, Iranian intelligence officials said they had arrested 15 people they called a "major terror and sabotage network with links to the Zionist regime". The group had plotted to assassinate an Iranian scientist in February, the authorities said.

Iranian officials have also accused Israel of infiltrating neighboring Azerbaijan to organize attacks against the Islamic Republic.

Unsubstantiated reports in the Iranian media earlier this month said Israel has pushed for the transfer Of 1,200 members of the exiled Iranian rebel group Mujahideen Khalq Organization (MKO) from their base in Iraq to Azerbaijan.

Late last year Israel distanced itself from the MKO´s efforts to be removed from the U.S. terrorism blacklist, saying it did not consider the group to be "an asset".

Iran denies Western accusations it is seeking to develop a nuclear weapons capability, but major powers are pushing Tehran to become more transparent and cooperative ahead of talks later this month.

Israel says it could attack Iran if it thinks that is the only way to stop it from getting nuclear arms.

British Foreign Secretary William Hague on Monday warned the European Union would impose tougher sanctions on Iran if it failed to take concrete steps to allay international concerns over its nuclear program. (© Thomson Reuters 2012. 05/15/12)