NEW : Magnetic explosives were used in other Iran assassinations , ambassador says . The Jerusalem Post reported Wednesday that the Israeli military chief of staff Benny Gantz , speaking at a Knesset Foreign Affairs and Defense Committee meeting , warned that `` 2012 will be a critical year in the connection between Iran gaining nuclear power , changes in leadership , continuing pressure from the international community and events that happen unnaturally . '' Secretary of State Hillary Clinton categorically denies U.S. involvement in the killing . An Israeli military spokesman says he does not know who carried out the attack . A bomb was put under Ali Ahmadi Roshan 's car , state - run IRNA news agency says .
NEW : Magnetic explosives were used in other Iran assassinations , ambassador says . Secretary of State Hillary Clinton categorically denies U.S. involvement in the killing . An Israeli military spokesman says he does not know who carried out the attack . A bomb was put under Ali Ahmadi Roshan 's car , state - run IRNA news agency says .