(CNN) -- Iran has hanged a man who was convicted of killing one of its nuclear scientists, state-run Press TV reported Tuesday.

Majid Jamali Fashi was convicted of the January 2010 killing of Massoud Ali Mohammadi, an Iranian university professor and a nuclear scientist. He was also convicted of spying. Prosecutors accused him of working for Israel´s spy agency, Mossad, and said he was paid $120,000 by Israel to carry out the hit.

Israel does not comment on such claims.

The killing was among a series of attacks against Iranian nuclear scientists in recent years.

In January, Iran sent a letter to the United Nations secretary- general alleging that the killings of the scientists were terrorist attacks that followed a clear pattern.

"There is firm evidence that certain foreign quarters are behind such assassinations," the letter said. "It is highly expected from the secretary-general of the United Nations, and President of the Security Council of the United Nations, as well as all other relevant organs and bodies, to condemn, in the strongest terms, these inhumane terrorist acts."

Mostafa Ahmadi Roshan, another nuclear scientist, was killed in a blast in Tehran in January after a motorcyclist placed a magnetic bomb under Roshan´s Peugeot 405 automobile. Mohammadi and one other scientist were killed in a similar fashion in the last two years.

With no one claiming responsibility, the killings remain shrouded in mystery.

In January, Mohammad Khazaee, Iran´s U.N. ambassador, blamed Israel for the attacks.

"They are trying to assassinate the Iranian scientists to deprive Iranians from the right of using peaceful nuclear energy," Khazaee said. "We believe that these terrorist attacks are supported by some elements -- especially within the Israeli regime, as well as some quarters around the world."

Israel generally refuses to comment on accusations and speculation. After Roshan´s death, Brig. Gen. Yoav Mordechai, a spokesman for the Israel Defense Forces, said on his Facebook page Wednesday, "I have no idea who targeted the Iranian scientist but I certainly don´t shed a tear."

Some in Iran have pointed to the United States, but U.S. Secretary of State Hillary Clinton rejected the claims.

"I want to categorically deny any United States involvement in any kind of act of violence inside Iran," she said in January. (© 2012 Cable News Network 05/15/12)