Iran says the killing of a young scientist Saturday was a "U.S.-Zionist terrorist act."
Darioush Rezai-Nejad, 35, was gunned down in Tehran on Saturday by assailants who also wounded his wife, according to state-run Iranian media.
A number of Iranian nuclear scientists have been attacked in recent years, but officials said in this case there may have been a mistake. Official media said Rezai-Nejad, a promising graduate student, may have been killed because his name is similar to another scientist, who does work on Iran's nuclear program.
Despite assassinations, cyberattacks and stringent sanctions, Iran continues to press ahead with its nuclear activity, which it says is peaceful. Tehran recently announced the installation of new, second-generation centrifuges that could accelerate the country's efforts to enrich uranium.