Iran has issued an impassioned letter to the United Nations Secretary General charging that the killings of Iranian nuclear scientists were terror 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 term, these inhumane terrorist acts." Mostafa Ahmadi Roshan, a nuclear scientist, was killed in a blast in Tehran on Wednesday morning, the latest in a series of attacks against such scientists in recent years. A motorcyclist placed a magnetic bomb under Roshan''s Peugeot 405. Two other scientists were killed in a similar fashion in the capital city in the last two years. Iran''s UN Ambassador Mohammad Khazaee blamed Israel for the attacks during an interview with CNN Wednesday night. "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," he said. Other government officials in Iran leveled the same accusation throughout the day Wednesday, with Iranian lawmaker Kazem Jalali blaming the intelligence agencies of the United States and Israel. The United Nations'' nuclear watchdog, the International Atomic Energy Agency, also bore responsibility for passing on information about Iran''s nuclear scientists to other countries, state-run IRNA news agency said. On Wednesday, US 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. "We believe there has to be an understanding between Iran, its neighbors and the international community that finds a way forward for it to end its provocative behavior, end its search for nuclear weapons and rejoin the international community and be a productive member of it." Israel does not normally comment on such claims. However, 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." Roshan, 32, was a deputy director for commercial affairs at the Natanz uranium enrichment facility in Isfahan province and a graduate of Iran''s Oil Industry University, according to the semi-official news agency Fars. Natanz, which is said to have 8,000 centrifuges in operation, is one of two facilities that is enriching uranium in the country. This week, the IAEA identified the second in the mountains of Qom province. The attack also comes at a time when relations between Iran and the United States have rarely been as strained. Iran sentenced Iranian-American and former Marine Amir Hekmati to death Tuesday for alleged espionage, prompting strong condemnation from the US State Department.