WASHINGTON - The United States denied any role in Wednesday's killing of an Iranian nuclear scientist, the latest in a series of events that have exacerbated tensions with Iran.
The assassination of Mostafa Ahmadi Roshan was the latest in a year that has already seen new U.S. economic sanctions, threats to bar American ships from the Persian Gulf, an Iranian death sentence to a jailed U.S. citizen and an escalation in Tehran's uranium enrichment program.
Iranian reports said two assailants on a motorcycle attached a magnetic bomb to Roshan's car, killing him and his driver. Roshan was a chemistry expert and director of the Natanz uranium enrichment facility in central Iran, and the slaying suggested a widening covert effort to set back the Islamic republic's atomic program.
But U.S. officials said they had nothing to do with it.
"I want to categorically deny any United States involvement in any kind of act of violence inside Iran," Secretary of State Hillary Rodham Clinton told reporters. "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."
Earlier, State Department spokeswoman Victoria Nuland wouldn't answer a question about whether Washington was involved in the killing - or if the administration viewed Roshan as an innocent victim. "I'm not going to speak to who may or may not have done this," she told reporters.
The attack also came one day after Israeli military chief Lt. Gen. Benny Gantz was quoted as telling a parliamentary committee that 2012 would be critical for Iran - in part because of "things that happen to it unnaturally."
And other Israeli officials, hinted at covert campaigns against Iran without directly admitting involvement.
"Many bad things have been happening to Iran in the recent period," said Mickey Segal, a former director of the Israeli military's Iranian intelligence department. "Iran is in a situation where pressure on it is mounting, and the latest assassination joins the pressure that the Iranian regime is facing."
Iranian authorities blamed Israel.
One former official said the magnetic-bomb attack does bear the hallmarks of an Israeli hit. Current and former U.S. officials say Washington prefers proxies like Israel to carry out operations inside Iran, and that up until two years ago, the U.S. and Israel coordinated actions against Iran closely. But the officials say the White House halted such cooperation after Israeli Prime Minister Benjamin Netanyahu took power.
The officials, past and present, spoke on condition of anonymity to discuss sensitive strategic negotiations.