The United States has denied any role in Wednesday's killing of an Iranian nuclear scientist in Tehran.
After the State Department initially declined to respond to Iranian charges that the U.S. or Israel was responsible for Mostafa Ahmadi Roshan's assassination, the White House said the United States "had absolutely nothing to do" with the blast that killed Roshan. White House spokesman Tommy Vietor said the U.S. strongly condemns the attack and all acts of violence.
U.S. Secretary of State Hillary Clinton repeated the White House denial of any U.S. involvement in the scientist's killing. "I want to categorically deny any United States involvement in any kind of act of violence inside Iran," she said.
Iranian media said Wednesday two unidentified people on a motorcycle attached a magnetic bomb to Roshan's car, killing him and his driver and wounding a passer-by.
In statements, Iran blamed the attack on Israel and the United States. Iran's vice president, Mohammad Reza Rahimi, told state television that the incident will not stop the country from advancing its nuclear activities.
Israel too denied responsibility. But on Tuesday, Israeli military chief Lieutenant General Benny Gantaz told lawmakers that 2012 would be a "critical year" for Iran because things would happen to the country in an unnatural way.
Also Wednesday, Iran sent a letter to United Nations Secretary-General Ban Ki-moon, expressing deep concern over "such cruel, inhumane and criminal acts of terrorism" against Iranian scientists. 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 and to take effective steps towards elimination of terrorism in all its forms and manifestations."
Iran's Fars agency said the 32-year-old Roshan supervised a department at the Natanz nuclear facility, Iran's main enrichment site. Iran has been enriching uranium to relatively low levels at the above-ground site.
Attackers have killed or wounded several Iranian nuclear scientists in recent years, including blasts in late 2010 that state media also attributed to bombs placed on cars by motorcyclists.