The Obama administration condemned an attack in Tehran that killed a nuclear scientist, and Iran threatened Israel with revenge.

Mostafa Ahmadi Roshan, 32, was killed Wednesday when a bomb placed on his car by a motorcyclist exploded. Roshan reportedly was a supervisor at the Natanz uranium enrichment facility, in addition to being a professor at Tehran’s technical university.

“We condemn any assassination or attack on an innocent person, and we express our sympathies to the family,” Victoria Nuland, the State Department spokeswoman, said Wednesday.

Tommy Vietor, the National Security Council spokesman, denied any U.S. role. “The United States had absolutely nothing to do with this,” he said. “We strongly condemn all acts of violence, including acts of violence like this.”

Iran blamed Israel for the attack and threatened revenge.

“The bomb was a magnetic one and the same as the ones previously used for the assassination of the scientists, and the work of the Zionists,” the semi-official Fars news agency quoted Tehran’s Deputy Governor Safarali Baratloo as saying. Fars called the explosion a terrorist attack.

Kayhan, a newsmpaper considered a mouthpiece for the theocracy, suggested retaliation.

“We should retaliate against Israel for martyring of our young scientist,” an editorial quoted by the New York Times said.

At least four Iranian nuclear scientists have been killed in anonymous attacks since January 2010. Iranian officials have blamed Israel and the United States for the attacks.

Iran’s Atomic Energy Organization said in a statement that the killing was “a heinous act” and that “We will continue our (nuclear) path without any doubt … Our path is irreversible,” Reuters reported.

Israeli media reported Tuesday that Israel Defense Forces’ Chief of General Staff Lt.-Gen. Benny Gantz said in an address to a closed Knesset committee that Iran should expect more “unnatural” events in 2012.

Iran’s top nuclear official said the country was about to start production at its second major uranium enrichment site.

Iran announced last week that it would begin uranium enrichment at an underground nuclear facility located near the holy city of Qom.

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